Causes of NeoplasiaThe origin for many neoplasms is obscure. However, there are several theories of origin:

Environmental causes:

Chemicals: including those that are man-made (such as aniline dyes and bladder cancer), drugs (cigarette smoke and lung cancer), and natural compounds (aflatoxins and liver cancer) which are carcinogenic.

Oncogenic viruses: such as human papillomavirus (HPV) implicated in most squamous cell carcinomas of cervix and anogenital squamous papillomas, Epstein-Barr virus (EBV) implicated in African Burkitt's lymphoma, and hepatitis B virus (HBV) implicated in development of hepatocellular carcinomas.

Radiation: including ultraviolet light that induces pyrimidine dimers in DNA and promotes skin cancers. Ionizing radiation (such as gamma radiation) induces mutations in DNA and promotes malignancies such as leukemia, thyroid, lung, colon, and breast cancers.

Chemical carcinogenesis

There are two steps: initiation and promotion An initiating carcinogenic agent irreversibly damages cell

DNA (it is mutagenic) to start the process. Examples of carcinogenic initiators include: alkylating agents like cyclophosphamide, polycyclic aromatic hydrocarbons like epoxides found in smoked foods, aromatic amines or

azo dyes used in food coloring, aflatoxins in moldy peanuts, nitrosamines in pickled foods.

A promoting agent (which may be the same as the carcinogen) then acts (reversibly) to cause proliferation of a neoplastic cell clone, but there appears to be a "dose-threshold" concentration of promoter below which neoplasia will not occur. Examples of promoters include: hormones such as estrogen, drugs such as diethylstilbesterol, and chemicals such as cyclamates used as sweeteners.

Hereditary causes:

Chromosomes which have absent or defective anti-oncogenes that control growth (retinoblastoma results from defective chromosome 13)

Obscure defects: racial predilections (American women have breast cancer more often than Japanese women; Japanese men have stomach cancer far more often than American men).

Age: older persons have a greater propensity to develop neoplasms from lack of effective control mechanisms.

Altered DNA:

All of the above are probably mediated by the cause, whatever it is, producing a mutation in, or damage to, cell DNA

There can be mutations involving tumor suppressor genes (such as p53), which then fail to exert a controlling influence upon growth activation.