Why screen for cancer?

Burden of Cancer

Cancer Registry

Cancer Incidence

Cancer Mortality

Cancer Prevalence

Screening for Cancer

Incidence

• Number of new cases diagnosed with a

disease (e.g. cancer) in a defined

population over a given period of time.

• Usually expressed as a rate e.g. per

100,000.

Benefits Cancer Incidence vs Mortality

Incidence

Counts cancers which are cured eg

skins

Event closer to risk factors especially if

long survival

Allows levels to be monitored

irrespective of treatment changes

Allows calculation of survival

Data cleaned more than deaths

Non-melanoma skin25%

Trachea, Bronchus & Lung13%

Prostate11%Colon

7%

Rectum4%

Stomach4%

Bladder3%

NHL3%

Kidney2%

Others28%

Most Common Cancers (Males)

Lung

24%

Stomach

4%

Other

25%

Leukaemia

3%NHL

3%Kidney

3%

Bladder

4%

Pancreas

4%

Oesophagus

6%

Colorectal

11%

Prostate

13%

Cancer deaths, males, UK,

2004

Cancer incidence, males, UK,

2004

Ovary

4%

Trachea, Bronchus &

Lung 8%

Breast

21%

Non-melanoma skin

26%

Others

22%

Rectum

3%

Colon

7%

NHL

3%

Uterus

3%

Malignant Melanoma

3%

Cancer incidence, females, UK,

2004

Most common Cancers (Females)

Colorectal

10%

Ovary

6%

Oesophagus

3%

Stomach

3%

Bladder

2%Leukaemia

3%NHL

3%

Pancreas

5%

Breast

17%

Lung

18%Other

29%

Cancer deaths, females, UK,

2004

Incidence Trends

Cancer Deaths

Mortality Trends

Prevalence

• Total number of cases (old and new) with a

disease (e.g. cancer) in a defined population

within a given period of time.

• Point prevalence – at a specific point in time

• Period prevalence – over a defined time period

• Usually expressed as a proportion/percentage.

Cancer Prevalence

26

1444

2544

377 470 490 475 453280 225 204 289 152 119 96 36 33

4186 1291

601 489 358188

609

150

510199 167 115

296114 78 91 38 20

0

500

1000

1500

2000

2500

3000

3500

4000

4500B

rea

st

Co

lore

cta

l

Pro

sta

te

Me

lan

om

a

Lym

ph

om

a

Lu

ng

He

ad

an

d N

eck

Ute

rus

Bla

dd

er

Ova

ry

Kid

ne

y

Le

uka

em

ia

Sto

ma

ch

Ce

rvix

Te

stis

Mu

ltip

le …

Oe

so

ph

ag

us

Bra

in

Pa

ncre

as

Liv

er

Cancer site

Prevalence of cancer in Northern Ireland: Diagnosed in 2000-2004, alive at the end of 2004

Female

Male

Mortality/Survival

Mortality rate: number of deaths caused by disease in a population over a specified time period. Usually expressed per 1000 or per 100,000 per year.

Survival rate: percentage of people within a specified population who are alive for a specified time period after diagnosis. Usually expressed as a five-year relative survival rate.

Survival Figure. 3.22: Age-Standardised relative survival for breast cancer by stage

Survival Figure. 3.22: Age-Standardised relative survival for prostate cancer by stage

Survival Figure. 3.22: Age-Standardised relative survival for colorectal cancer by stage

Survival Figure. 3.22: Age-Standardised relative survival for lung cancer by stage

Screening - scrutiny of people in

order to detect the presence of

disease, disability or other

attributable under study.

Rationale - Early diagnosis leads

to more effective treatment and a

greater cure rate.

Types of Screening

Type A Screening to detect early stage or

asymptomatic disease - e.g.

Mammogram.

Type B Screening detects a precancerous

state e.g. cervical cancer.

Screening Test

Cheap, quick, acceptable.

Reliable (same result if repeated).

Validity (how good is test at

discriminating who has the disease from

those who do not). Measured using

Sensitivity and Specificity.

Trends in Cervical Cancer Mortality

http://www.qub.ac.uk/research-centres/nicr/FileStore/PDF/Filetoupload,176739,en.pdf

What cancers do we screen for?

Breast Cancer

Cervical Cancer

Colorectal cancer

No screening – ovary marker CA125

-- liver markers afp,CA125,

-- prostate marker PSA

Negative Effects of Screening

Hazards from screening test, e.g. Radiation.

Reliance on false negatives so ignoring symptoms.

Anxiety and additional tests for false positives.

Opportunity Costs.

Creating ‘patients’ from well people.

Anxiety and interventions in those whom disease will never

kill.

Risk from interventions.

Anxiety in those who choose to ignore invitation.

Over diagnosis.

World age-standardised incidence and

mortality rates for prostate cancer for

selected countries, estimates for the year 2000