knowles_introduction to the cellular and molecular biology of cancer 4th ed

Introduction to the Cellular and Molecular Biology of Cancer

Margaret A. Knowles Peter J. Selby

OXFORD UNIVERSITY PRESS

Introduction to the Cellular and Molecular Biology of Cancer

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Introduction to the Cellular and Molecular Biology of CancerMargaret A. Knowles Peter J. SelbyCancer Research UK Clinical Centre, St Jamess University Hospital, Leeds

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Great Clarendon Street, Oxford OX2 6DP Oxford University Press is a department of the University of Oxford. It furthers the Universitys objective of excellence in research, scholarship, and education by publishing worldwide in Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With ofces in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Oxford is a registered trade mark of Oxford University Press in the UK and in certain other countries Published in the United States by Oxford University Press Inc., New York # Oxford University Press 2005, Fourth Edition The moral rights of the authors have been asserted Database right Oxford University Press (maker) Fourth edition rst published 2005 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, or under terms agreed with the appropriate reprographics rights organization. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this book in any other binding or cover and you must impose the same condition on any acquirer British Library Cataloguing in Publication Data (Data available) Library of Congress Cataloging in Publication Data Knowles, Margaret A. Introduction to the cellular and molecular biology of cancer / Margaret A. Knowles, Peter J. Selby. p. cm. ISBN 0-19-852563-X (alk. paper) ISBN 0-19-856853-3 (alk. paper) 1. CancerMolecular aspects. 2. Cancer cells. I. Selby, P. (Peter) II. Title. RC268.5.K56 2005 616.99 0 4071dc22 2004030576 Typeset by Newgen Imaging Systems (P) Ltd., Chennai, India Printed in Great Britain on acid-free paper by Antony Rowe, Chippenham ISBN 0-19-856853-3 (Hbk) 978-0-19-856853-7 ISBN 0-19-852563-X (Pbk) 978-0-19-852563-9 10 9 8 7 6 5 4 3 2 1

Preface to the fourth edition

The rst edition of this book, published in 1985 was a testimony to the dramatic molecular revolution that was taking place in biology and consequently in cancer research at that time. The book evolved from a series of introductory lectures developed to help new students and research fellows that came to work at the Imperial Cancer Research Fund Laboratories in London to assimilate the rapidly evolving body of knowledge on cancer. These popular talks were designed to give the non-expert a background to related areas of research and were given by experts from within the Imperial Cancer Research Fund, many of whom subsequently contributed chapters to the rst edition of the book. Twenty years later, the need for a comprehensive introduction to this broad eld is even more apparent and the introductory lectures at what is now the Cancer Research UK London Research Institute continue and are as popular as ever. Today, laboratory science has begun to have a real impact on clinical medicine and it is of utmost importance that scientists have not only a broad view of laboratory cancer research but also a good understanding of the most up to date treatment options. Similarly, it is essential that clinicians treating the various types of neoplastic disease are aware of developments in basic science and can apply these appropriately. It is our view that only when determined attempts to bridge the gap between the laboratory and clinic are made by both clinicians and scientists that rapid translation will take place. Our objective has been to facilitate acquisition of basic information on all aspects of cancer research to facilitate this process. Inevitably over the years, many authors of this book have changed, some topics have become less relevant and new topics have been added. However, we are delighted that the initiator of the series and one of the editors of the rst three editions of the book has given advice during the planning of this fourth edition and has again contributed to the

rst chapter of the book. Sammy Franks was Ph.D. supervisor to one of us (MK) and throughout his career has encouraged young scientists to look beyond the topic of their personal Ph.D. or postdoctoral project to encompass the wider picture. His care in selection of topics and authors for the earlier editions of the book generated a comprehensive and readable text that has been used extensively. In preparing this new edition we have tried to keep his original goals in mind. Our task in updating this has not been easy, not least because of the unprecedented developments in many areas of biology. There are many more relevant and indispensable topics than before and this creates a conict with the size limitations for a textbook of this kind. Perhaps the most difcult aspect of modern biology, however, is the complexity of current knowledge that seems to defy simplication to the level of the non-expert. Inevitably, this is more apparent in some areas than in others and we are aware that the factual content of the book has increased enormously. The modern cell or molecular biologist faces a challenging initiation into the eld of cancer research. Ultimately, however, the dramatic increase in knowledge provides young scientists today with the power to understand and manipulate the fundamental processes of life as never before. We believe, and hope, that the reader will nd, that the obvious benets in understanding complex biological problems far outweigh the effort required to assimilate the increased information content of this volume. We have expanded the number of chapters from 22 to 30 to include chapters that cover some of the new technologies such as global analyses of the genome, transcriptome, and proteome and more recent concepts and discoveries in cell biology such as the process of apoptosis, the rapid advances made in understanding the nite or innite proliferative capacity of somatic cells and the

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PREFACE TO THE FOURTH EDITION

epigenome. Huge strides have been made in our understanding of genomic alterations in cancer cells and these are reected in an extensively updated chapter on molecular cytogenetics. All chapters with similar titles to the previous edition have been completely rewritten or extensively updated. On reviewing the nal content of the book, one of the most striking changes is the general acceptance by authors of the identity of the key genes affecting the processes they seek to elucidate. No longer is identication of genes a critical issue but the (almost entire) sequence of the human genome now allows biologists to focus on biological processes rather than detective work designed to nd genes. One of the striking observations is the diversity of types of genes involved in cancer development that is reected in several chapters. Similarly, developments in novel cancer therapies now draw on many areas of molecular biology and several are now represented as separate chapters. This is indeed a

period of plenty in terms of what is known and what is possible and the scope for new scientists and clinicians to draw on this is unprecedented. Authorship for this edition continues to represent experts in each eld of research but this now extends beyond the connes of a single organization to draw on expertise from around the world. The assembly of such an impressive group of experts in such a fast-moving area of research ensures that the content is as up-to-date as possible and we are indebted to all contributors for their efforts. Inevitably, there will be omissions and imbalances that will be felt more acutely by some readers than others and we encourage readers to comment and make suggestions for any future editions of the book.

Leeds January 2005

M. A. K. P. J. S.

Preface to the third edition

Successive editions of this book have mirrored developments in cancer research and we hope that this new edition will achieve our original objective of providing a relatively brief but comprehensive introduction to the initiation, development, and treatment of cancer. On this background we have tried to provide an introduction to the results and new developments in the eld using the current techniques of cell and molecular biology. A fuller understanding of the detail in some chapters needs a basic knowledge of molecular biology which can be found in several textbooks (e.g. Lodish et al., 1995) but the general principles in each chapter should be comprehensible without this. This edition has allowed us to bring up-to-date information in elds in which there has been great activity and even some achievement. In particular, the chapters concerned with epidemiology, genetic and chromosome changes, oncogenes, chemical and radiation carcinogenesis, growth factors, the biology of human leukaemia, and hormones and cancer, and the Glossary have been rewritten or extensively revised. Other chapters have been brought up-todate and new chapters on cytokines and cancer, the molecular pathology of cancer, cancer prevention, and screening have been added. Gene nomenclature may cause some confusion since although there is now a standardized format it is not yet generally accepted by all workers in the eld. Many of the genes and oncogenes described by some earlier workers have retained their original format for historical reasons. Some genes were discovered in mouse cells, others in humans, and still others in viruses, and different names were given to genes which are now known to be essentially the same. Genes described for human cells are* He was complaining to his wife about his porridge. She hit him on the head.

now usually written in upper case, italic type and their protein products in roman type. Mouse genes are often given in lower case italic type, their products as for those of human genes; those from Drosophilia are italicized with only the rst letter capitalized. Specic oncogenes may be cited by a lower case rst letter (c for cellular, v for viral), followed by a hyphen, and then the gene name in italic type. However, there may be further modier terms. For the most part, we have tried to maintain some degree of consistency but in some chapters we have retained the original format if this is still used by many workers. The apparently inevitable increase in girth that seems to accompany middle age has had its effect on the book which is somewhat larger than its predecessors but we hope that the increase in information will compensate. As one of the philosophers in The Crock of Gold (Stephens 1931) commented Perfection is nality; nality is death. Nothing is perfect. There are lumps in it.* No doubt there are lumps, and errors, and omissions in this new edition. We should be pleased to have comments and suggestions for their correction.

ReferencesLodish, H., Baltimore, D., Berk, A., Zipursky, S. L., Matsudaira, P., Darnell, J. (1995). Molecular Cell Biology. Scientic American Books, W. H. Freeman, New York. Stephens, J. (1931). The Crock of Gold. Macmillan, London.

London June 1996

L. M. F. N. M. T.

Preface to the second edition

The second edition of this bookprepared sooner than we had expectedhas given us an opportunity to correct some of the faults and errors pointed out by our readers and reviewers, as well as allowing us to bring the book up-to-date in a number of areas in which there have been rapid developments. In particular the chapters on the genetic and chromosomal changes, growth factors, immunotherapy, and epidemiology have been expanded and more information on viral and chemical carcinogenesis added to the appropriate sections. We have also claried and added new information to most of the other chapters. At some stage all authors and editors of introductory textbooks are faced with the awful choice of deciding what to leave out. When does completeness conict with comprehension? Is the

omission of this and that piece of information really a mortal sin or could the distinguished reviewer who pointed it out just happen to have been told about it by a passing graduate student? In the end of course we did what all editors must do and made our own choice. We hope that this second edition will continue to be of use to its readers as an introduction to cancer studies and as a source of further information either in key references or in specialized reviews such as Cancer Surveys. We should still appreciate comments and suggestions for further improvement. London January 1990 L. M. F. N. M. T.

Preface to the rst edition

Cancer holds a strange place in modern mythology. Although it is a common disease and it is true to say that one person in ve will die of cancer, it is equally true to say that four out of ve die of some other disease. Heart disease, for example, a much more common cause of death, does not seem to carry with it the gloomy overtones, not always justiable, of a diagnosis of cancer. This seems to stem largely from the fact that we had so little knowledge of the cause of a disease which seemed to appear almost at random and proceed inexorably. At the turn of the century, when the ICRF was founded (in 1902), the clinical behaviour and pathology of the more common tumours was known but little else. Over the years clinicians, laboratory scientists and epidemiologists established a rm database. The behaviour patterns of many tumours, and in some cases even the causal agents, were known but how these agents transformed normal cells and inuenced tumour cell behaviour remained a mystery. The development of molecular biology opened up a major new approach to the molecular analysis of normal and tumour cells. We can now ask and begin to answer questions particularly about the genetic control of cell growth and behaviour that have a bearing on our understanding not only of the family of diseases that we know as cancer but of the whole process of life itself. It is this, as much as nding a cause and cure for the disease, that gives cancer research its importance. The initiating event which ultimately led to the publication of this book was the realization that many graduate students and research fellows who came to work in our Institute, although highly specialized in their own elds, had relatively little knowledge of cancer and there were few suitable textbooks to which they could be referred. Consequently, regular introductory courses were organized for new staff members at which experts were asked to give a general introduction to their

particular eld of study. The talks were designed to give a background for the non-expert, as for example, molecular biology for the morphologist or cell biology for the protein chemist. The courses proved to be very popular. This book follows a similar pattern and has many of the same contributorshence the fact that most are, or have been, connected with the Imperial Cancer Research Fund. After a general introduction describing the pathology and natural history of the disease, each section gives a more detailed, but nevertheless general, survey of its particular area. We have tried to present principles rather than a mass of information, but inevitably some chapters are more detailed than others. Each chapter gives a short list of recommended reading which provides a source for seekers of further knowledge. The topics covered have been selected with some care. Although some, particularly those concerned with treatment, may not at rst glance appear to be directly related to cell and molecular biology, we feel that a knowledge of the methods used must give a wider understanding of the practical problems which may ultimately prove to be solvable by the application of modern scientic technology. On the other hand, knowledge of inherent cell behaviour (e.g. radiosensitivity, cell cycling, development of drug resistance, etc.) is important for the design of novel therapeutic approaches that rely less on empirical considerations. Despite differences in the levels of technical details presented in some chapters, we hope that all are comprehensible. We have provided a fairly comprehensive glossary so that if some terms are not explained adequately in the text, do try the glossary. Finally, the editors would appreciate any comments, suggestions or corrections should a second edition prove desirable. London December 1985 L. M. F. N. M. T.


Contents

Contributors 1 What is cancer? Leonard M. Franks and Margaret A. Knowles 2 The causes of cancer Naomi Allen, Robert Newton, Amy Berrington de Gonzalez, Jane Green, Emily Banks, and Timothy J. Key. 3 Inherited susceptibility to cancer D. Timothy Bishop 4 DNA repair and cancer Beate Koberle, John P. Wittschieben, and Richard D. Wood 5 Epigenetic events in cancer Jonathan C. Cheng and Peter A. Jones 6 Molecular cytogenetics of cancer Denise Sheer and Janet M. Shipley 7 Oncogenes Margaret A. Knowles 8 Tumour suppressor genes Sonia Lan and David P. Lane 9 The cancer cell cycle Chris J. Norbury 10 Cellular immortalization and telomerase activation in cancer Robert F. Newbold 11 Growth factors and their signalling pathways in cancer Sally A. Prigent

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45 61

78 95 117 135 156

170 186

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CONTENTS

12 Apoptosis: molecular physiology and signicance for cancer therapeutics Dean A. Fennell 13 Mechanisms of viral carcinogenesis Paul Farrell 14 Cytokines and cancer Peter W. Szlosarek and Frances R. Balkwill 15 Hormones and cancer Charlotte L. Bevan 16 The spread of tumours Ian Hart 17 Tumour angiogenesis Kiki Tahtis and Roy Bicknell 18 Stem cells, haemopoiesis, and leukaemia Mel Greaves 19 Animal models of cancer Jos Jonkers and Anton Berns 20 The immunology of cancer Peter C. L. Beverley 21 The molecular pathology of cancer Tatjana Crnogorac-Jurcevic, Richard Poulsom, and Nicholas R. Lemoine 22 From transcriptome to proteome Silvana Debernardi, Rachel A. Craven, Bryan D. Young, and Rosamonde E. Banks 23 Local treatment of cancer Ian S. Fentiman 24 Chemotherapy D. Ross Camidge and Duncan I. Jodrell 25 Radiotherapy and molecular radiotherapy Anne Kiltie 26 Monoclonal antibodies and therapy Tom Geldart, Martin J. Glennie, and Peter W. M. Johnson 27 Immunotherapy of cancer Andrew M. Jackson and Joanne Porte

210 229 242 257 278 289 305 317 337 356

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390 399 414 428 443

CONTENTS

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28 Cancer gene therapy John D. Chester 29 Screening Peter Sasieni and Jack Cuzick 30 Conclusions and prospects Peter Selby and Margaret Knowles Index

458 480 503 506


Contributors

Naomi Allen, Cancer Research UK, Epidemiology Unit, University of Oxford, Gibson Building, Radcliffe Inrmary, Oxford OX2 6HE, [email protected] Frances Balkwill, Translational Oncology Laboratory, Barts and the London, Queen Marys School of Medicine and Dentistry, The John Vane Science Centre, Charterhouse Square, London EC1M 6BQ, [email protected] Emily Banks, National Centre for Epidemiology & Population Health, Australian National University, Canberra, ACT 0200, Australia, [email protected] Rosamonde Banks, Cancer Research UK Clinical Centre, St Jamess University Hospital, Beckett Street, Leeds LS9 7TF, [email protected] Amy Berrington de Gonzalez, Cancer Research UK Epidemiology Unit, University of Oxford, Oxford OX2 6HE, [email protected] Anton Berns, The Netherlands Cancer Institute, Division of Molecular Genetics, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands, [email protected] Charlotte Bevan, Department of Cancer Medicine, Imperial College London, 5th Floor Laboratories, MRC Cyclotron Building, Du Cane Road, London W12 0NN, [email protected] Peter Beverley, The Edward Jenner Institute for Vaccine Research, Compton, Newbury, Berkshire RG20 7NN, [email protected] Roy Bicknell, Cancer Research UK, Angiogenesis Laboratory, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DS, [email protected]

Tim Bishop, Cancer Research UK, Genetic Epidemiology, St. Jamess University Hospital, Beckett Street, Leeds LS9 7TF, [email protected] Ross Camidge, Edinburgh Cancer Centre, Western General Hospital, Edinburgh EH4 2XU, [email protected] Jonathan Cheng, USC/Norris Cancer Center, 1441 Eastlake Avenue, Los Angeles, CA 9033, USA, [email protected] John Chester, Cancer Research UK Clinical Centre, St Jamess University Hospital, Beckett Street, Leeds LS9 7TF, [email protected] Rachel Craven, Cancer Research UK Clinical Centre, St Jamess University Hospital, Beckett Street, Leeds LS9 7TF, [email protected] Tatjana Crnogorac-Jurcevic, Barts and the London, Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, [email protected] Jack Cuzick, Cancer Research UK, Centre for Epidemiology, Mathematics and Statistics, Wolfson Institute for Preventive Medicine, Barts and the London, Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, [email protected] Silvana Debernardi, Department of Medical Oncology, Barts and The London, Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, [email protected] Paul Farrell, Ludwig Institute for Cancer Research, Department of Virology, Imperial College, St. Marys Campus, Norfolk Place, London W2 1PG, [email protected]

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CONTRIBUTORS

Dean Fennell, Northern Ireland Thoracic Oncology Research Group, Cancer Research Centre, University Floor, Belfast City Hospital, Lisburn Road, Belfast BT9 7AB, Northern Ireland, [email protected] Ian Fentiman, Academic Oncology, 3rd Floor, Thomas Guy House, Guy s Hospital, St. Thomas Street, London SE1 9RT, [email protected] L. M. Franks, 13 Allingham Street, London, N1 8NX, [email protected] Tom Geldart, Cancer Research UK Oncology Unit, Cancer Sciences Division, Southampton University School of Medicine, Southampton General Hospital, Southampton SO16 6YD, [email protected] Martin Glennie, Tenovus Laboratory, Cancer Sciences Division, Southampton University School of Medicine, Southampton General Hospital, Southampton SO16 6YD, [email protected] Mel Greaves, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, [email protected] Jane Green, Cancer Research UK Epidemiology Unit, University of Oxford, Oxford OX2 6HE, [email protected] Ian Hart, Department of Tumour Biology, Barts and The London, Queen Marys School of Medicine and Dentistry, John Vane Science Centre, Charterhouse Square, London EC1M 6BQ, [email protected] Andrew Jackson, Genitourinary Cancer Immunotherapy Program, Duke University Medical Centre, Durham, NC2 7710, USA, [email protected] Duncan Jodrell, University of Edinburgh Cancer Research Centre, Crewe Road South, Edinburgh EH4 2XR, [email protected] Peter Johnson, Cancer Research UK Oncology Unit, Cancer Sciences Division, Southampton University School of Medicine, Southampton General Hospital, Southampton SO16 6YD, [email protected]

Peter Jones, USC/Norris Cancer Center, 1441 Eastlake Avenue, Los Angeles, CA 90033, USA, [email protected] Jos Jonkers, The Netherlands Cancer Institute, Division of Molecular Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands, [email protected] Timothy Key, Cancer Research UK, Epidemiology Unit, Gibson Building, Radcliffe Inrmary, Oxford OX2 6HE, [email protected] Anne Kiltie, Cancer Research UK Clinical Centre, St Jamess University Hospital, Beckett Street, Leeds LS9 7TF, [email protected] Margaret Knowles, Cancer Research UK Clinical Centre, St. Jamess University Hospital, Beckett Street, Leeds LS9 7TF, [email protected] Beate Koberle, University of Pittsburgh Cancer Institute, Hillman Cancer Center, 5117 Centre Avenue, Research Pavilion, Suite 2.6, Pittsburgh, Pa, 15213-1863, USA, [email protected] Sonia Lan, Department of Surgery and Molecular Oncology, Nine Wells Hospital Medical School, University of Dundee, Dundee DD1 9SY, [email protected] David Lane, Department of Surgery and Molecular Oncology, Nine Wells Hospital Medical School, University of Dundee, Dundee DD1 9SY, [email protected] Nicholas Lemoine, Cancer Research UK, Molecular Oncology Unit, Barts and the London, Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, [email protected] Robert Newbold, Brunel Institute of Cancer Genetics and Pharmacogenomics, Brunel University, Uxbridge UB8 4SP, [email protected] Robert Newton, Cancer Research UK Epidemiology Unit, University of Oxford, Oxford OX2 6HE, [email protected] Chris Norbury, Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, [email protected]

CONTRIBUTORS

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Joanne Porte, Department of Reproductive Endocrinology, University of North Carolina, Chapel Hill, NC27599, USA Richard Poulsom, In Situ Hybridisation Service Histopathology Unit, Cancer Research UK, 44 Lincolns Inn Fields, London, WC2A 3PX, [email protected] Sally Prigent, Department of Biochemistry, Room 201E, Adrian Building, University of Leicester, University Road, Leicester LE1 7RH [email protected] Peter Sasieni, Cancer Research UK, Centre for Epidemiology, Mathematics and Statistics, Wolfson Institute for Preventive Medicine, Barts and the London, Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, [email protected] Peter Selby, Cancer Research UK Clinical Centre, St. Jamess University Hospital, Beckett Street, Leeds LS9 7TF, [email protected] Denise Sheer, Cancer Research UK London Research Institute, Human Cytogenetics Laboratory, Lincolns Inn Fields Laboratories, 44 Lincolns Inn Fields, London WC2A 3PX, [email protected] Janet Shipley, Molecular Cytogenetics, The Institute of Cancer Research, 15 Cotswold Road,

Belmont, Sutton, Surrey SM2 5NG, [email protected] Peter Szlosarek, Translational Oncology Laboratory, Cancer Research UK, Barts and The London, Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, [email protected] Kiki Tahtis, Cancer Research UK, Angiogenesis Laboratory, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DS, [email protected] John Wittschieben, University of Pittsburgh Cancer Institute, Hillman Cancer Center, 5117 Centre Avenue, Research Pavilion, Suite 2.6, Pittsburgh, Pa, 15213-1863, USA, [email protected] Richard Wood, University of Pittsburgh Cancer Institute, Hillman Cancer Center, 5117 Centre Avenue, Research Pavilion, Suite 2.6, Pittsburgh, Pa, 15213-1863, USA, [email protected] Bryan Young, Department of Medical Oncology, Barts and The London, Queen Marys School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, [email protected]


CHAPTER 1

What is cancer?Leonard M. Franks and Margaret A. Knowles

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

1.9

1.10

1.11 1.12 1.13 1.14 1.15 1.16

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Normal cells and tissues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control of growth in normal tissues . . . . . . . . . . . . . . . . . . . . . . . . . . The cell cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tumour growth or neoplasia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The process of carcinogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.1 Genes involved in carcinogenesis . . . . . . . . . . . . . . . . . . . . . . Factors influencing the development of cancers . . . . . . . . . . . . . . . . . Genetic instability, clonal selection, and tumour evolution . . . . . . . . . 1.8.1 Selection of altered clones . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8.2 Tumour clonality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tumour diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9.1 Benign tumours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9.2 Malignant tumours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tumour nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.1 Tumours of epithelium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.2 Tumours of mesenchyme . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.3 Tumours of the haemato-lymphoid system . . . . . . . . . . . . . . . 1.10.4 Tumours of the nervous system . . . . . . . . . . . . . . . . . . . . . . . 1.10.5 Germ cell tumours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10.6 Tumours showing divergent differentiation . . . . . . . . . . . . . . 1.10.7 Tumour staging and the spread of tumours (metastasis) . . . . . How tumours present: some effects of tumours on the body. . . . . . . . How does cancer kill? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Treatment of cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cancer prevention and screening. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental methods in cancer research . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1 2 3 4 4 5 6 7 9 10 12 15 15 16 16 17 19 19 19 20 20 21 21 21 22 22 23 23

1.1 IntroductionCancer has been known since human societies rst recorded their activities. It was well known to the ancient Egyptians and to succeeding civilizations but, as most cancers develop in the latter decades of life, until the expectation of life began to increase from the middle of the nineteenth century onwards, the number of people surviving to this age was relatively small. Now that the infectious diseases, the major causes of death in the past, have been

controlled by improvements in public health and medical care, the proportion of the population at risk of cancer has increased dramatically. Although diseases of the heart and blood vessels are still the main cause of death in our ageing population, cancer is now a major problem. At least one in three will develop cancer and one in four men and one in ve women will die from it. For this reason, cancer prevention and control are major health issues. However, cancer research has wider signicance.1

2

CELLULAR AND MOLECULAR BIOLOGY OF CANCER

Cancer is not conned to man and the higher mammals but affects almost all multicellular organisms, plants as well as animals. Since it involves disturbances in cell proliferation, differentiation, and development, knowledge of the processes underlying this disease help us to understand the very basic mechanisms of life. About 140 years ago a German microscopist, Johannes Mueller, showed that cancers were made up of cells, a discovery which began the search for changes which would help to pinpoint the specic differences between normal and cancer cells. In the intervening period a huge amount of information has been acquired about the cancer cell. In the past two decades in particular, rapid technological progress has allowed us to begin to dissect the cancer genome, transcriptome, and proteome in unprecedented detail and today there seems no limit to the amount of information that can be obtained. However, this does not naturally answer all of the questions posed by those early cancer biologists. Some fundamental questions remain unanswered, despite our technical prowess and the availability of commercial kits for most basic assays. Even the most advanced technology is of no value if it is not applied appropriately and it is still too early for the benets of some recent technical advances to be clear. In the past, some of the major questions for the cancer biologist concerned what types of experiments were possible and the development of new techniques to extend these possibilities formed a major part of the work done. Now that almost anything seems technically possible, the key issue for the twenty-rst century biologist is to identify the right questions to ask. This can make the difference between a deluge of uninterpretable data and a real improvement in understanding. This book does not aim to identify what these right questions are but to provide an introduction to current understanding of cancer, its causes, biology, and treatment. However, we do indicate areas in which new and exciting discoveries are being made and those in which key questions remain unanswered. Cancer is a disorder of cells and although it usually appears as a tumour (a swelling) made up of a mass of cells, the visible tumour is the end result of a whole series of changes which may have taken many years to develop. In this chapter, we discuss in general terms what is known about the changes that take place during the process of tumour development, consider tumour diagnosis

and nomenclature, and provide some denitions. Succeeding chapters deal with specic aspects in more detail.

1.2 Normal cells and tissuesThe tissues of the body can be divided into four main groups: the general supporting tissues collectively known as mesenchyme; the tissue-specic cellsepithelium; the defence cellsthe haematolymphoid system; and the nervous system. The mesenchyme consists of connective tissue broblasts which make collagen bres and associated proteins, bone, cartilage, muscle, blood vessels, and lymphatics. The epithelial cells are the specic, specialized cells of the different organs, for example, skin, intestine, liver, glands, etc. The haemato-lymphoid system consists of a wide group of cells, mostly derived from precursor cells in the bone marrow which give rise to all the red and white blood cells. In addition, some of these cells (lymphocytes and macrophages) are distributed throughout the body either as free cells or as xed constituents of other organs, for example, in the liver, or as separate organs such as the spleen and lymph nodes. Lymph nodes are specialized nodules of lymphoid cells, which are distributed throughout the body and act as lters to remove cells, bacteria, and other foreign matter. The nervous system is made up of the central nervous system (the brain and spinal cord and their coverings) and the peripheral nervous system, which is comprised of nerves leading from these central structures. Thus, each tissue has its own specic cells, usually several different types, which maintain the structure and function of the individual tissue. Bone, for example, has one group of cells responsible for bone formation and a second group responsible for bone resorption and remodelling when the need arises, as in the repair of fractures. The intestinal tract has many different epithelial cell types responsible for the different functions of the bowel, and so on. The specic cells are grouped in organs which have a standard pattern (Figure 1.1). There is a layer of epithelium, the tissue-specic cells, separated from the supporting mesenchyme by a semipermeable basement membrane. The supporting tissues (or stroma) are made up of connective tissue (collagen bres) and broblasts (which make collagen), which may be supported on a layer of muscle and/or bone depending on the organ. Blood

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Differentiated cells

EpitheliumStem cells

Nerve

Basement membrane Blood vessels Muscle

Collagen fibres Mesenchyme Fibroblast

Figure 1.1 A typical tissue showing epithelial and mesenchymal components.

vessels, lymphatic vessels, and nerves pass through the connective tissue and provide nutrients and nervous control among other things for the specic tissue cells. In some instances, for example, the skin and intestinal tract, the epithelium which may be one or more cells thick depending on the tissue, covers surfaces. In others it may form a system of tubes (e.g. in the lung or kidney), or solid cords (e.g. liver), but the basic pattern remains the same. Different organs differ in structure only in the nature of the specic cells and the arrangement and distribution of the supporting mesenchyme.

1.3 Control of growth in normal tissuesThe mechanism of control of cell growth and proliferation is one of the most intensively studied areas in biology. It is important to make the distinction between the terms growth and proliferation. Growth is used here to refer to an increase in size of a cell, organ, tissue, or tumour and proliferation to an increase in the number of cells by division. Growth is often used as a loose term for both of these processes but the distinction is particularly important now that factors controlling both of these processes are becoming clear. In normal development and growth there is a very precise mechanism that allows individual organs to reach a xed size, which for all practical purposes, is never exceeded. If a tissue is injured, the surviving cells in most organs begin to divide to replace the damaged cells. When this has been completed, the process stops, that is, the normal control mechanisms

persist throughout life. Although most cells in the embryo can proliferate, not all adult cells retain this ability. In most organs there are special reserve or stem cells, which are capable of dividing in response to a stimulus such as an injury to replace organ-specic cells. The more highly differentiated a cell is, for example, muscle or nerve cells, the more likely it is to have lost its capacity to divide. In some organs, particularly the brain, the most highly differentiated cells, the nerve cells, can only proliferate in the embryo, although the special supporting cells in the brain continue to be able to proliferate. A consequence of this, as we shall see later, is that tumours of nerve cells are only found in the very young and tumours of the brain in adults are derived from the supporting cells. In other tissues there is a rapid turnover of cells, particularly in the small intestine and the blood and immune system. A great deal of work has been done on the control of stem cell growth in the red and white cells (haemopoietic system), and the relationship of the factors involved in this process to tumour development (Chapter 18). For reasons that are still unclear, rapid cell division itself is not necessarily associated with an increased risk of tumour development, for example, tumours of the small intestine are very rare. In the embryo there is a range of stem cells, some cells capable of reproducing almost any type of cell and others with a limited potential for producing more specic cells, for example, liver or kidney. In the adult, there is now unequivocal evidence for the existence of stem cells capable of perpetuating themselves through self-renewal to generate

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specialized cells of particular tissues. Striking parallels exist between the properties of stem cells and cancer cells. This, together with the potential for the use of human stem cells in various types of regenerative medicine, makes this a very active area of research (Reya et al., 2001). Control of organ or tissue size is achieved via a ne balance between stimulatory and inhibitory stimuli. When the balance is shifted, for example, when the tissue is damaged and repair is needed, when a specic physiological stimulus is applied, for example, hormonal stimulation or because extra work is required from an organ, the component cells may respond in one of two ways to achieve these objectives. This may be by hypertrophy, that is, an increase in size of individual components, usually of cells which do not normally divide. An example is the increase in size of particular muscles in athletes. The alternative is hyperplasia, that is, an increase in number of the cells. When the stimulus is removed, commonly the situation returns to the status quo as exemplied by the rapid loss of muscle mass in the lapsed athlete. Some of the stimuli that lead to these compensatory responses are well-known growth factors and hormones that are discussed in more detail in Chapters 11, 14, and 15. Recent work on the insulin/IGF (insulinlike growth factor) system, particularly in the fruit y Drosophila, has demonstrated that this plays a pivotal role in the control of organ and organism size (Oldham and Hafen, 2003). It is of note that several molecules involved in these processes are known to act as oncogenes or to be dysregulated in cancer. For example, IGFs are commonly overexpressed and the phosphoinositide 3-kinase (PI3K) pathway, which is activated by insulin/IGF signalling, is functionally disrupted in various ways in cancer cells (Vivanco and Sawyers, 2002).

are recognized: G1, S, G2, and M. Following a proliferative stimulus, G1 is a gap or pause after stimulation where little seems to be happening. However, if the cell is destined to divide, there is much biochemical activity in G1 in preparation for DNA replication. S is the phase of DNA synthesis, where the chromosomes are replicated and other cell components also increase. G2 is a second gap period following DNA synthesis and M is the stage of mitosis in which the nuclear membrane breaks down and the condensed chromosomes can be visualized as they pair and divide prior to division of the cytoplasm to generate two daughter cells. A further cell cycle phase is recognized, G0, which is a resting phase in which non-cycling cells rest with a G1 DNA content. Progression through the cell cycle is now known to be restricted at specic checkpoints, one in G1 and others in S and G2/M. These provide an opportunity for cells to be diverted out of the cycle or to programmed cell death (apoptosis) if, for example, there is DNA damage or inappropriate expression of oncogenic proteins. Disruption of these cell cycle checkpoints or alterations to key cell cycle proteins are found in many, if not all, cancers. A detailed discussion of the cell cycle, its regulation and disruption in cancer is given in Chapter 9.

1.5 Tumour growth or neoplasiaIt is not possible to dene a tumour cell in absolute terms. Tumours are usually recognized by the fact that the cells have shown abnormal proliferation, so that a reasonably acceptable denition is that tumour cells differ from normal cells in their lack of response to normal control mechanisms. Since there are almost certainly many different factors involved, the altered cells may still respond to some but not to others. A further complication is that some tumour cells, especially soon after the cells have been transformed from the normal, may not be dividing at all. In the present state of knowledge any denition must be operational. Given these qualications we can classify tumours into three main groups: (1) Benign tumours may arise in any tissue, grow locally, and cause damage by local pressure or obstruction. However, the common feature is that they do not spread to distant sites. (2) In situ tumours usually develop in epithelium and are usually but not invariably, small. The cells

1.4 The cell cycleThe way in which cells increase in number is similar for all somatic cells and involves the growth of all cell components (increase in cell mass) followed by division to generate two daughter cells. Although the structural changes which take place during this process, the cell cycle, have been known for many years, our current detailed knowledge of the molecular basis of the process has only been acquired in the past two decades. Four stages

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have the morphological appearance of cancer cells but remain in the epithelial layer. They do not invade the basement membrane and supporting mesenchyme. Various degrees of dysplasia, that is, epithelial irregularity but not identiable as cancer in situ are recognized in some tissues and these may sometimes precede cancer in situ. Theoretically, cancers in situ may arise also in mesenchymal, haemato-lymphoid, or nervous tissue but they have not been recognized. (3) Cancers are fully developed (malignant) tumours with a specic capacity to invade and destroy the underlying mesenchyme (local invasion). The tumour cells need nutrients via the bloodstream and produce a range of proteins that stimulate the growth of blood vessels into the tumour, thus allowing continuous growth to occur (Chapter 17). The new vessels are not well formed and are easily damaged so that the invading tumour cells may penetrate these and lymphatic vessels. Tumour fragments may be carried in these vessels to local lymph nodes or to distant organs where they may produce secondary tumours (metastases) (Chapter 16). Cancers may arise in any tissue. Although there may be a progression from benign to malignant, this is far from invariable. Many benign tumours never become malignant. Some of these problems of denition may be more easily understood if we consider the whole process of tumour induction and development (carcinogenesis).

1.6 The process of carcinogenesisCarcinogenesis (the process of cancer development) is a multistage process (Figure 1.2). In an animal, the application of a cancer-producing agent (carcinogen) does not lead to the immediate production of a tumour. Cancers arise after a long latent period and multiple carcinogen treatments are more effective than a single application. Experiments carried out on mouse skin in the 1940s by Berenblum and Shubik (reviewed by Yuspa, 1994) indicated that at least three major stages are involved. The rst was termed initiation and was found to involve mutagenic effects of the carcinogen on skin stem cells. The second stage, which can be induced by a variety of agents that are not directly carcinogenic in their own right, was termed promotion. Following chronic treatment of carcinogen-initiated mouse skin with promoting agents, papillomas (benign skin tumours) arise. The major effect of promoters seems to be their ability to promote clonal expansion of initiated cells. Finally in the third stage, progression, some of these benign tumours either spontaneously or following additional treatment with carcinogens, progress to invasive tumours. The terms coined to describe this animal model are still commonly applied to describe the process of carcinogenesis in man. The mouse skin model indicated that carcinogenesis is a multistep process and clearly this is

Accumulation of heritable changes

Ca in situ

Tumour invasion

Clinical tumour

Epithelium Mesenchyme Muscle

Metastasis possible 0 20 years

Figure 1.2 Tumour development showing progression from normal to invasive tumour via accumulation of heritable changes over a long period of time. The rate of acquisition of these changes will be inuenced by environmental exposures and host response.

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also the case for human cancer. For example, most solid tumours of adults arise in the later decades of life, usually a long time after exposure to a specic carcinogenic insult or after a long period of continuous exposure and this can be explained in terms of the requirement for several distinct heritable changes. The nature of some of these changes is now known in detail and is discussed at length in several of the following chapters. These include genetic alterations to proto-oncogenes and tumour suppressor genes (Chapters 7 and 8) and epigenetic alterations (Chapter 5). Histopathological observations also provide evidence for a long preneoplastic period, sometimes with morphologically identiable lesions such as benign tumours or in situ dysplasia, which may persist for many years and within which a malignant tumour eventually arises. The latent period between initiation and the appearance of tumours is great. In man, after exposure to industrial carcinogens, it may take over 20 years before tumours develop. Even in animals given massive doses of carcinogens, it may take up to a quarter or more of the total lifespan before tumours appear. The requirement for acquisition of multiple events is the likely explanation for this. In the tumour that nally emerges, most of the genetic and epigenetic changes seen are clonal, that is they are present in the entire population of cells. It is likely that a series of selective phases of clonal expansion takes place in the tumour such that after each event, there is outgrowth of a clone of cells with a selective advantage. Evidence for this has come from studies on many tissues and particularly where areas of surrounding tissue or multiple related lesions can be sampled at surgery. In these circumstances, it is common to nd several shared clonal events in different lesions and occasionally in the apparently normal surrounding epithelium and additional events in the most histopathologically advanced lesion (see Section 1.8.1).

1.6.1 Genes involved in carcinogenesisSeveral types of genes are now known to contribute to the development of cancer. The discovery that the oncogenes of tumour-producing retroviruses are related to cellular genes (proto-oncogenes) (Chapter 7) has led to intensive research into the role of these genes in normal and tumour cell growth, proliferation, and differentiation. Many cellular genes can act as oncogenes when expressed

inappropriately or mutated. These genes act in a dominant way at the cellular level to drive proliferation or prevent normal differentiation. This dominant mode of action makes oncogenes attractive potential targets for specic cancer therapies and there is currently a huge effort to inhibit the activity of specic oncogenes using a variety of approaches, some of which are already bearing fruit (Druker and Lydon, 2000). An interesting question in this regard concerns the role of such genes in the initiation, progression, and maintenance of tumours. In mouse skin, for example, mutational activation of a ras oncogene is an initiating event and subsequent tumour progression and metastasis appear to depend on sequential incremental levels of expression of the gene which is clearly required for tumour maintenance. Similarly it has been shown in mouse models of melanoma that expression of a ras transgene is required for tumour maintenance. However, in this model, examples of escape of tumours in which ras gene expression had been switched off (Chin and DePinho, 2000), raises the possibility that not all genetic events required early in tumour development may be required later in the process, a fact that represents a caveat in the design of oncogenetargeted therapies. Genes that provide negative regulatory signals in the normal cell are also implicated in the development of cancer. If such a gene requires loss or inactivation to contribute to the transformation process, then it is likely that both copies of the gene must be altered and that such tumour suppressor genes would be genetically recessive at the cellular level. It was proposed by Knudson that two independent mutations are needed for the development of inherited cancers. In such cases of inherited (familial) tumour predisposition, the rst mutation is present in the germ cells (sperm or ovum) and is therefore inherited by every cell in the body (Chapter 3). Only one further somatic mutation is required for complete gene inactivation in these cases. In the more common non-familial cancers, two somatic mutations in the gene are required and the chances of this happening in the same cell are much less. Many tumour suppressor genes have now been identied and many appear to conform to Knudsons so-called Two-hit hypothesis (reviewed in Knudson, 1996). Several mechanisms of inactivation of the two alleles have been described and these are discussed in detail in Chapters 5 and 8. Not surprisingly however, there

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are exceptions to this rule and there are several examples where loss of function of one allele of a tumour suppressor gene is sufcient to generate an altered cell phenotype that can contribute to transformation. This is termed haploinsufciency and as discussed in Chapter 8, the levels of protein required for adequate function may vary from gene to gene, leading to the prediction that some genes will be more strongly haploinsufcient than others. In normal cells, the requirement for efcient repair mechanisms is clear. In the absence of such repair capacity, it is difcult to see how long-lived species such as man could survive daily exposure to environmental carcinogens without severe toxicity and inevitably a high cancer rate. The mechanisms of repair of different types of DNA damage have now been elucidated in great detail both in lower organisms and in mammalian systems. There are several familial syndromes in which components of the DNA repair machinery are mutated in the germline and these have provided valuable tools for discovery of the mechanisms of repair of different types of DNA lesions. One of the consequences of altered repair capacity is an increased risk of cancer. This class of cancercausing genes can be referred to as mutator genes as their altered function leads to an increased capacity for mutation of other genes. Any alteration in the function of such genes, however small, has the capacity to alter an individuals lifetime risk of cancer. However, in contrast to the tumour suppressor genes, replacement of the function of these genes has no direct effect on tumour phenotype. There is currently much interest in identifying not only highly penetrant mutations in DNA repair and carcinogen-metabolizing genes but also the less penetrant polymorphisms that affect each individuals response to environmental damage. DNA repair and its relationship to cancer development are discussed in detail in Chapter 4. Other mutator genes include genes involved in regulation of the mitotic apparatus which can also affect the rate of acquisition of other mutations. An example is aurora kinase A (AURKA) also known as STK15, a gene whose product associates with the centrosome in S phase and appears to play a role in centrosome separation, duplication, and maturation. This gene is amplied and overexpressed in several types of cancer and this is associated with the generation of aneuploidy (deviation from the normal diploid number of chromosomes) (Dutertre et al., 2002). Other genes

which also lead to aneuploidy when altered include the mitotic checkpoint genes BUB1 and BUBR1 both of which can be classied as tumour suppressor genes as inactivation is required for phenotypic effect. This last example indicates that some subdivision within the large grouping of tumour suppressor genes is possible. This has led to invention of the terms gatekeeper and caretaker to describe these different suppressor roles (Kinzler and Vogelstein, 1998). Gatekeeper genes are dened as rate-limiting for a step in the pathway of tumour development. Thus, the adenomatous polyposis coli gene APC is considered to be an initiation gatekeeper as its inactivation is required early in colorectal carcinogenesis. Caretaker genes include those which when functionally inactivated lead to defective DNA repair or other loss of function that leads to mutation, for example, some DNA repair genes, BUB1 and BUBR1. Finally, the ability of the immune system to detect and destroy altered cells that are identied as non-self (immune surveillance) may have an impact on cancer incidence. For some time it has been proposed that tumour cells expressing antigens that are recognized by the immune system will be eradicated at an early, preclinical stage and only those cells not eliciting such a response can survive to generate a clinically detectable tumour. This may be reected in the difculty in prompting a patient to mount a response against their tumour. However, it is still not clear how much impact this theoretical effect has on tumour incidence, nor whether specic defects in the immune system have a major impact (see Chapters 20 and 27).

1.7 Factors inuencing the development of cancersMany factors are involved in the development of cancer. These include both endogenous factors such as inherited predisposition and exogenous factors such as exposure to environmental carcinogens and infectious agents. All of these factors are discussed in depth in Chapters 2, 3 and 13. Another factor not discussed in detail elsewhere in the book and which has a clear inuence on the type of cancer which develops is age. In fact, age is the biggest risk factor for developing cancer (Figure 1.3). There is an age-associated, organspecic tumour incidence. Most cancers in man

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350 300 Rate per 100,000 250 200 150 100 50 0 20 25 30 35 40 45 50 55 60 65 70 75 80 Age groupFigure 1.3 An example of age-specic cancer incidence rate. Colon cancer incidence in men in England in 1999.

and experimental animals can be divided into three main groups depending on their age-specic incidence: (1) Embryonic tumours, for example, neuroblastoma (tumours of embryonic nerve cells), embryonal tumours of kidney (Wilms tumours), retinoblastoma, etc. (2) Tumours found predominantly in the young, for example, some leukaemias, tumours of the bone, testis, etc. (3) Those with an increasing incidence with age, for example, tumours of prostate, colon, bladder, skin, breast, etc. The juvenile onset of some cancers such as some leukaemias and those described as embryonal, is believed to reect the requirement for only a limited number of alterations. Some of them such as familial retinoblastoma, originate in cells that already contain one inherited genetic defect and if only one or two further events is required for tumorigenicity of a target cell (e.g. inactivation of the second allele of RB), tumour development becomes almost inevitable given the large number of essentially initiated cells present. There are several possible molecular and physiological explanations for the last group of ageassociated tumours (group 3) which include the most common adult human cancers. First, in the normal individual there is continuous exposure throughout life to low levels of exogenous carcinogens and it is likely that it is both the time required for accumulation of multiple genetic changes and for multiple phases of clonal selection that results in tumours only later in life. This is

probably a major factor in determining the age association of most epithelial tumours. A second possibility is that with age there are changes in the cellular environment that are more permissive for outgrowth of altered clones or which allow or encourage neoplastic change to take place, for example, alterations in the immune or hormonal systems or changes in the tissue microenvironment. The relationship of tumour development in endocrine-sensitive organs such as the breast or prostate to age-associated hormonal changes in the patient is still to be completely dened but seems likely to be involved in the rate of growth of these tumours. One of the roles of hormones is to stimulate division of hormone-sensitive cells, that is, these may act as a promoting agent (Chapter 15). There is some debate about whether the relative decline in function of the immune system in old age plays a role and this is discussed in Chapter 20. Interestingly, there is also recent evidence that senescenceassociated changes that occur in mesenchymal cells can affect adjacent epithelial cells and this may have a promoting effect. Senescent broblasts express several enzymes involved in extracellular matrix remodelling, for example, MMP-9 and stromelysin and it has been hypothesized that the ageing stroma may contribute to epithelial carcinogenesis in this way (Krtolica and Campisi, 2003). Some elegant experiments have been carried out by Cunha and colleagues which identify important effects of tumour stromal cells. They studied the effect of stromal cells derived from prostate tumours or from normal prostate on the in vivo growth of preneoplastic prostate epithelial cells in tissue recombination experiments. In combination with

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tumour stroma, the preneoplastic epithelium was able to form carcinomas, whereas when combined with normal stroma, only normal ductular structures were formed indicating that, even though non-tumorigenic themselves, stromal cells derived from the tumour microenvironment had lost the ability to exert their normal inhibitory control over the epithelial component of the tissue. Thus, normal age-associated changes and acquired changes in the tumour stroma can contribute to epithelial carcinogenesis. Finally, it is possible that there are age-associated changes in some cells which increase their susceptibility to neoplastic transformation. Ageassociated decline in DNA repair capacity with associated increase in mutation rate could be considered as such a factor. Although certain mutations can themselves alter this capacity, it is not clear whether changes in basal mutation rate can account in any signicant measure for the ageassociated increase in tumour incidence. There is some evidence that certain types of damage are repaired less efciently by cells derived from old tissues. For example, UV-induced damage is repaired less efciently by skin broblasts from old donors than from young donors. These differences may make a minor contribution to carcinogenesis in the old but are clearly not the major drivers. There is some experimental evidence for an increased sensitivity to carcinogen-induced neoplastic change in tissue cultures and in transplants derived from some organs from old animals, but it is not clear how much this is related to the presence of cells in old tissues which have already sustained genetic damage. Interestingly, tumours that develop in aged laboratory mice are more frequently haematological and mesenchymal cell tumours than the epithelial types seen in man. Until recently this has been an unexplained observation. However, recent results provide a highly plausible explanation. As described in Chapter 10, the ends of mammalian chromosomes contain telomeric repeat sequences that with each normal round of DNA replication, lose some sequence due to the end-replication problem. Thus, telomere length decreases with successive divisions and with age. It is now known that normal human cells, which show a nite lifespan in vitro, enter a phase commonly known as crisis when they are stimulated by certain viral oncogenes (for example, SV40 large T) to continue proliferation

beyond their normal senescence limit. At crisis, telomere length is severely shortened, rendering the telomeres vulnerable to end-to-end fusion and subsequent chromosomal breakage at mitosis. This can generate some of the typical cytogenetic abnormalities seen in epithelial tumours. Such tumours therefore bear the cytogenetic hallmarks of telomere attrition. Escape from crisis occurs only when cells begin to express telomerase, the specialized reverse transcriptase that allows them to maintain telomere length. The likely explanation for the species-specic age-associated tumour spectrum is that mice have very long telomeres which unlike human telomeres never undergo critical shortening within the lifespan of the organism, nor within the additional proliferative lifespan required for tumour development. Somatic mouse tissues also express telomerase. Hence the tumours that develop do not show major chromosomal rearrangements. So why do they develop mesenchymal tumours and leukaemias? The answer may lie in the requirement for fewer genetic events for transformation of these cell types.

1.8 Genetic instability, clonal selection, and tumour evolutionOur recent ability to dissect the cancer genome at both the gross chromosomal and nucleotide level has revealed extensive genetic change. Often this is complex, particularly in advanced epithelial cancers and is commonly referred to as genetic or genomic instability. Recent studies have revealed that genetic instability can take distinct forms and a debate has arisen over whether these represent cause or effect. One type of instability is that which results from inactivation of mismatch repair (MMR) genes such as MSH2 and MLH1 (Chapter 4). Defects in MMR lead to numerous changes in short simple sequence repeats spread throughout the genome (called microsatellites; MMR is also termed microsatellite instability, MIN). MIN is characteristic of tumours found in patients with hereditary non-polyposis colorectal cancer (HNPCC) who inherit mutations in MSH2 or MLH1. Interestingly, MIN tumours usually have a diploid karyotype which contrasts with non-MIN epithelial cancers which commonly show complex karyotypic abnormalities, commonly termed chromosomal instability (CIN). The causes

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of CIN have been less obvious. There are several possibilities including alterations in mitotic checkpoint genes or genes involved in centrosome function or chromosomal segregation as discussed above. Already some tumours have been found to contain this type of alteration. It is also possible that once a cell has become aneuploid by chance, this in itself predisposes it to become even more aneuploid. This might happen, for example, at mitosis where segregation of aberrant or large numbers of chromosomes is more error-prone. A nal mechanism is the inherent CIN which is generated in cells at senescence when chromosomes have severe telomere attrition. As indicated above, shortening of telomeres in advance of re-expression of telomerase can lead to severe chromosomal rearrangement via end-to-end fusion followed by breakage at segregation. There is evidence for all of these mechanisms and it is likely that one or more may contribute to the development of any given tumour and that the mechanism that is active will shape the genome in specic and recognizable ways that may well be tissue or tumour type specic. More detailed analysis of tissue samples taken throughout the course of tumour development should help to clarify these issues in the next few years. While it is clear that tumours often have MIN or CIN, it is not yet clear whether this is an early event in the process, nor whether it is necessary for tumour development. It has been argued that the probability of tumours acquiring the necessary number of genetic alterations is too low without some additional mutator effect. This type of calculation is difcult and to date no clear answer is apparent, though there is no doubt that some tumour cells have this phenotype while others, particularly early in their development, have little genomic alteration that can be identied. It is probable however, that the level of generation of mutations is critical and that too much instability is likely to impede tumour development rather than promote it. Already it is known that the type of genetic instability present in the tumour cell has an effect on the type of mutation found. Thus, for example, MIN colorectal tumours tend to inactivate the two alleles of the APC gene via two point mutations, whereas CIN tumours tend to have one point mutation and one allele lost by deletion. Two recent reviews explore these concepts in depth using what is known about colorectal

carcinogenesis, possibly the best-studied model system, as an example (Rajagopalan et al., 2003; Sieber et al., 2003).

1.8.1 Selection of altered clonesThe process by which cancer cells develop and spread involves not only mutation but also selection of altered clones. These processes are the drivers of tumour evolution. It is thought that repeated rounds of mutation and selection occur during somatic evolution of a tumour. As the lineage evolves, the tumour cells acquire increased autonomy and eventually the capacity for metastasis. This is often compared to Darwinian evolution where in this case the ttest cell survives and multiplies. The low rate of mutation, calculated as 2 10 7 per gene per cell division for cultured human cells (Oller et al., 1989) precludes the acquisition by a single cell of multiple mutations simultaneously. Even when large carcinogen doses are applied, the large number of potentially lethal mutations sustained at the same time as any set of mutations with potential advantage is likely to lead to cell death rather than instant tumorigenicity. Thus the expectation is that events occur singly and in a particular sequence in each cancer. This is frequently referred to as a genetic pathway or progression pathway and for several cancer types attempts have been made to map the pathway in genetic terms. As indicated above, colorectal cancer is arguably the best elucidated model in this regard (Ilyas et al., 1999). In the colon, mutation of the APC gene is the initiating event. The resulting early adenoma then commonly acquires mutations in KRAS, SMAD4, and TP53, respectively as it progresses histopathologically via intermediate and late adenoma to carcinoma. The frequency of each of these changes in each of the lesion types suggests that there is a preferred order of events in this case but this does not appear to be invariable. Results from other tumour types where samples can be obtained from lesions at different stages in the process, or from cancers with different malignant potential, also show shared lesions and temporal ordering of events in some cases. There is also evidence that alternative pathways can lead to the same result, and in different tissues specic mechanisms may dominate. For example, many tumours show inactivation of TP53 via mutation while some others show amplication of the

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negative regulator of p53, MDM2. In the Rb pathway, some tumours show direct mutation of RB while others show inactivation of the pathway via inactivation of the negative regulator p16. The order of events may differ in different tissues. For example, mutations of TP53 are found frequently in lung cancer but patients with a germline mutation in TP53 (LiFraumeni syndrome) do not develop lung cancer as part of the syndrome. Possibly this reects inability of loss of p53 function to act early in the pathway to lung cancer but its suitability as an early event in the other tumours that develop in these LiFraumeni patients. The ultimate result of clonal evolution is escape from the normal growth restraints imposed on the cell in its normal tissue milieu. It follows therefore that the way in which this is achieved will depend to a great extent on what those growth restraints are. Hence the nding of tissue- and cell typespecic genetic alterations, different timing of alterations, etc. It is easy to envisage selection of mutations that increase proliferation or allow resistance to apoptosis or any of the other key features of cancer cells. However, mutations that increase mutation frequency such as those that generate CIN or MIN do not in themselves confer an immediate advantage to the cell. At present, it is not clear how such a phenotype is selected. One plausible explanation is that such mutations may occur rarely in the same cell as a second mutation that does confer an immediate advantage and thus are selected as passenger or bystander events. Many forms of treatment, for example, radiation and chemotherapy may provide additional mutagenic and selective stimuli and may precipitate the emergence of more aggressive variants. An obvious example is the destruction of X-ray-sensitive cells by X-ray treatment. If the tumour also contains X-ray-resistant cells, the cancer cells which are left after treatment will be X-ray resistant. Although progression is usually towards greater malignancy, this is not invariably so. There are a number of cases, unfortunately small, in which rapidly growing tumours have ceased to grow or even disappeared completely. Although we do not yet have a full explanation for this, some studies indicate that this may be related to the development of anti-tumour immunity in the host. Thus, a series of changes occur in a cell as carcinogenesis proceeds. As the tumour progresses, more and more normal characteristics are lost and

it is common to observe what has been described as dedifferentiation within the tumour tissue. This refers to the loss of normal structure and cellular functions characteristic of the tissue. Specialized products of the cell, for example, secretions or structural components may no longer be produced as the cell begins to take on new characteristics. The loss of normal differentiated features is referred to by a pathologist as anaplasia and the degree of such changes identied in tissue sections is used by the pathologist to grade tumours. In general, less well-differentiated tumours have a poorer prognosis than those that retain the differentiated characteristics of the normal tissue. As a rule, there is an approximate correlation between tumour grade and growth rate. The most differentiated tumours (low grade, i.e. Grade I) tend to be more slow-growing and the most anaplastic (high grade, i.e. III or IV) the more rapidly growing. Human breast cancers are graded in this way and it has been shown that about 80% of patients with welldifferentiated Grade I breast cancers will be alive and well at ve years (and often much longer) but only 20% of patients with Grade IV tumours will survive for this time. It is of course equally obvious from these gures that although 80% of patients with Grade I cancers survive, 20% with the same structural type of tumour do not. Tumour growth and progression is inuenced by factors other than tumour structure, and these may range from the rate of mutation and type of mutation they contain to the reaction of the patients own defence mechanisms. In recent years much effort has been made to identify additional tests that can be carried out in the pathology laboratory at the time of tumour diagnosis to add both diagnostic and prognostic (predictive) information and the search for molecular markers (proteins or DNA changes) that can supplement the repertoire of morphological tests is intense. These are discussed at length in Chapter 21. In fact, there are many examples of success in identifying such markers for use in tumour classication, prediction of prognosis or response to therapy, disease monitoring, and markers that can be used as therapeutic targets. These are described in several of the other chapters of this book. Possibly, the identication of such markers has been the earliest and most clinically applicable result of the intense effort of the past two decades to characterize human tumours at the molecular level. More successes will undoubtedly follow.

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1.8.2 Tumour clonalityWe have alluded to clonal evolution during tumour development but what of the origin of the tumour? Tumour clonality refers to the cellular origin of cancers. A monoclonal tumour develops from a single progenitor cell and a polyclonal tumour develops from multiple cells. In many tissues, a solitary primary tumour is the norm and this may or may not recur or progress. In this circumstance the question of clonality concerns only this single tumour and its direct descendents. However, in some tissues the situation is more complex and when the structure of the organ is examined in detail widespread abnormal pathology may be found. In such a tissue multicentric tumours are sometimes found. Could there be many cells involved in the generation of a tumour or does each tumour arise from a single initiated cell? The appearance of multiple preneoplastic lesions in a tissue has been described as a eld change. Figures 1.4 and 1.5 illustrate such a possible eld effect. These tissues show a gradation from benign

to malignant (as in Figure 1.2) but here the progression is in space rather than time. This has been particularly described in tissues such as the bladder, colon, oesophagus, and oral mucosa where there is a large epithelial surface available for study and in which essentially all of the cells have received similar exposure to environmental agents. Here the question of clonality can be addressed to each individual tumour that arises, that is, tumour clonality, but of equal interest both to biologist and clinician, is the relationship between all the lesions in a single patient. This can be referred to as the clonality of the disease. With the advent of molecular genetic techniques there has been an explosion of information concerning the genetic relationship of such synchronous lesions. There are several possibilities based on the clonality of each lesion and of the overall disease in the patient: (1) Each individual tumour consists of lineages derived from multiple normal parent cells. Such

b a c

dFigure 1.4 Section of the edge of a squamous cell carcinoma of skin, with normal skin (a) on the left and increasing dysplasia (b) and (c) leading into the main mass of the tumour (d) below right. Stained with haematoxylin and eosin (50).

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(a)

(b)

(c)

(d)

Figure 1.5 Detail of the areas marked in Figure 1.4 at higher magnication. (a) Normal skin (compare with Figure 1.1) showing mesenchyme below covered by normal epithelium with basal cells, more differentiated supercial cells and on top, layers of keratin formed from the supercial cells (360), (b) Dysplastic skin. There is an increase in the number of basal cells, which are more irregular than in the normal and there is a disturbance in the formation of keratin, which is clumped into an irregular dark mass in the surface layer instead of the more regular sheets in (a), that is, differentiation is disturbed, (c) Cell overgrowth. The cells themselves are abnormal; they vary in shape and size, the nuclei are much larger than normal and some are deeply stained. The usually distinct separation between epithelium and stroma is not seen, suggesting that invasion may be taking place. The cells are still recognizable as skin cells. This would be diagnosed as a moderately well-differentiated squamous carcinoma (360). (d) The centre of the tumour is made up of a mass of irregular spindle-shaped cells with no recognizable skin features. This would be diagnosed as an anaplastic (undifferentiated) carcinoma (360).

a tumour would be described as polyclonal. A tumour derived from a few parent cells would be termed oligoclonal. (2) Each tumour has a single parental cell of origin and multiple tumours in the same organ arise via seeding or direct spread of cells. Each is therefore a monoclonal tumour and this is monoclonal disease. (3) The disease is polyclonal, that is, more than one initiated cell progresses to generate multiple tumours each of which is derived from a single cell (monoclonal). There is in fact evidence for all three situations, though the majority of human cancers are solitary tumours of monoclonal origin and there is ongoing

debate over whether true polyclonal tumours do exist (Garcia et al., 2000). The methods most commonly used to assess tumour clonality are X-chromosome inactivation and loss of heterozygosity (LOH) analysis by microsatellite typing. During the course of embryonic development in females, genes on one of the X chromosomes are silenced by methylation of cytosine residues in the promoter (Chapter 5). Such methylation is heritably maintained and prevents transcriptional activation within the promoter region. This process is random and in any tissue, 50% of cells have methylation of each copy of X. A monoclonal tumour will therefore have inactivation of any gene on only one of its X chromosomes and this can be detected at the molecular level.

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Polymorphisms in X-linked genes have been used to identify individual parental alleles and when assessed in combination with the use of methylationsensitive restriction endonucleases, which cut only non-methylated DNA, assays for allelespecic methylation can be developed. Several X-chromosome loci have been used including glycerophosphate kinase (PGK), hypoxanthine phosphoribosyltransferase (HPRT), and the androgen receptor gene (HUMARA) (Vogelstein et al., 1987). Such analyses are restricted to female tissues and to those women who are heterozygous at the locus of choice, namely those that have distinguishable maternal and paternal alleles. While there are some problems in interpretation of X-inactivation assays for clonality, these assays have the signicant advantage that the feature studied is not itself part of the neoplastic process. Microsatellite typing uses the polymerase chain reaction (PCR) reaction to amplify short DNA products containing simple sequence repeats that are highly polymorphic in the human genome. Because the repeat length varies, alleles inherited from each

parent are frequently distinguishable by size. In a tumour with genomic deletion, for example, deletion of one copy of a tumour suppressor gene, loss of one allele (LOH, loss of heterozygosity) at nearby microsatellite repeats is commonly found in the tumour. Indeed this method has been widely used to map the locations of novel tumour suppressor genes. However, the use of this assay or any tumourspecic molecular alteration to assess clonality per se is somewhat restricted. For example, LOH analysis cannot detect true cellular polyclonality since LOH in a mixed population is difcult to detect. When tumour-specic genetic markers are used for clonality analysis, it is predicted that in related monoclonal tumours, markers associated with changes that occurred early in tumour development will show greatest concordance and those that occur later in tumour development may show divergence in related tumours that have undergone clonal evolution. This latter observation can be referred to as sub-clonal evolution. LOH analysis has been used to assess the temporal sequence of genetic events that has taken place during the

Initiated cell

9q-

Year 1

Preneoplastic epithelium

9q11p-

Year 10

Low-grade tumour

9q11p4p-

9q11p4p-

Year 15

High-grade invasive tumour

9q11p4p18qTP53 mut 1

9q11p6q8p-

9q11p6q17p-

Year 17

Metastatic tumour

9q11p6q17pTP53 mut 2

Year 18

Figure 1.6 Example of possible evolution of a metastatic tumour from a single initiated cell, over the course of many years. Changes shown are common deletions that may be identied by LOH analysis and different mutations in TP53 (TP53 mut 1 and 2). 9q-, 11p-, etc. denote deletions of the long (q) or short (p) arms of different chromosomes. Sub-clonal evolution within the population may lead to several distinct but spatially related tumours that differ in some but not all genetic changes. A nal event in one cell may allow a metastatic clone to evolve.

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evolution of a tumour from a series of temporally or spatially related lesions. Examples of such studies include the elucidation of neoplastic lineages in Barrett oesophagus (Barrett et al., 1999) and in synchronous and metachronous bladder cancer (Takahashi et al., 1998). An example of the type of lineage deduced from such studies is shown in Figure 1.6. Not only does information about the relationships between such lesions give valuable biological information about disease development but it also provides information with potential clinical application. For example, the presence of multiple different tumour clones within an epithelium may show a relationship to tumour recurrence rate or time to recurrence and may indicate a need for more vigilant monitoring. In the future, as targeted therapies become available, knowledge of the specic molecular characteristics of all tumours present, may inuence choice of therapy and polyclonal tumours may be more difcult to target in this way. By the time a tumour is detectable clinically, whether it has arisen from one or many cells, it has been present for a long time and the cells have had to go through a large number of cell divisions. A tumour of about 0.5 cm in diameter, which is just detectable, may contain over 500 million cells. Within such a population, even if deemed monoclonal by X-inactivation and other genetic assays, it is likely that at any point in time a large tumour could contain many potential new sub-clones with potential to evolve and some already forming sizeable sub-clones. Certainly, tumours show morphological differences in different regions and these can be accompanied by changes in protein expression detected by immunohistochemistry or other assays.

purposes, the two techniques used are tumour grading and tumour staging. Tumour grading attempts to measure the degree of dedifferentiation in tumours and is based on histological and cytological criteria (Figures 1.4 and 1.5). Histological differentiation is concerned with alterations in the structure of the tissue, that is, the relationship of cells to each other and to their underlying stroma. Cytological grading is based on the application of similar criteria to the structure of the specic tumour cells. Tumour staging assesses the extent of spread of tumours. Ideally, a range of objective molecular markers that can be added to this routine morphological assessment is highly desirable. To date such objective markers do not exist for all applications. However, as discussed in Chapters 6 and 21 there has been great progress in recent years in adding to the routine morphological assessment, a variety of assays based on our accumulating knowledge of the molecular biology of cancer. Many such tests are still at the experimental stage but some are in widespread application in the pathology or cytogenetics laboratory. For example, the differential diagnosis of many haematological malignancies routinely uses specic antibody panels for immunohistochemistry and/or the detection of specic chromosomal translocations in the genome. More details of these and other assays are given in Chapters 6 and 21 and here we will only discuss morphological assessment which is applicable to all neoplasms. Several papers have been written on tumour diagnosis by international panels of tumour pathologists. The following brief survey will only give a guide. We have chosen some of the examples, not because they are common, but because they illustrate particular points more clearly than the more common tumours.

1.9 Tumour diagnosisThere are no absolute methods for diagnosing and assessing the degree of malignancy of tumours. Microscopic examination of tissue is still the mainstay for routine use and the role of the pathologist at the time of diagnosis is critical. The pathologist has to decide whether the structure of the cells in the tissue is sufciently removed from the normal to allow a diagnosis of neoplasia and if so, whether the tumour is benign or malignant, its probable cell of origin, its degree of differentiation, and its extent of spread. For practical

1.9.1 Benign tumoursBenign tumours usually resemble their tissue of origin but every tissue component need not be involved and the cells may or may not be in their normal relationship. Benign tumours arise in most tissues, increase in size, but do not invade. They are usually separated from the surrounding normal tissue by a capsule of connective tissue. Cytologically, the specic tumour cells do not differ substantially from the structure of the normal organ cells. Benign tumours of bone or cartilage may produce nodules of bone or cartilage indistinguishable

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knowles_introduction to the cellular and molecular biology of cancer 4th ed

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