Cancer epidemiology - cancer epidemiology biomarkers and prevention

In most patients the cause of their cancer remains unknown and is probably multifactorial. Several environmental factors have, however, been identified as being associated with the development of malignancy.

Tobacco

The incidence of lung cancer in both men and women has increased dramatically in the last 25 years. The association of smoking with lung cancer is now indisputable and causative mechanisms have been identified: cigarette tobacco is responsible for one-third of all deaths from cancer in the UK. Smoking not only causes lung cancer, it is also associated with cancer of the mouth, larynx, oesophagus and bladder. As a consequence of public health campaigns, cigarette consumption in the UK is now beginning to decrease in men but not yet in women, in whom the incidence of lung cancer is still rising.

Alcohol

Alcohol is associated with cancers of the upper respiratory and gastrointestinal tracts, but it also interacts with tobacco in the aetiology of these tumours. It may be associated with an increased risk of breast cancer.

Diet

Dietary factors have been attributed to account for a third of cancer deaths, although it may be difficult to differentiate these from other epidemiological factors. For example, the incidence of stomach cancer is particularly high in the Far East, while breast and colon cancers are more common in the western, economically more developed countries. Many associations have been observed without a causative mechanism being identified between the incidence of cancer and the consumption of dietary fibre, red meat, saturated fats, salted fish, vitamin E, vitamin A and many others.

Ultraviolet light

Ultraviolet light is known to increase the risk of skin cancer (basal cell, squamous cell and melanoma). The incidence of melanoma is therefore particularly high in the white Anglo-Celtic population of Australia, New Zealand and South Africa, where exposure to UV light is combined with a genetically predisposed population.

Occupational factors

In 1775, Percival Pott described the association between carcinogenic hydrocarbons in soot and the development of scrotal epitheliomas in chimney sweeps. Subsequently, other chemicals have been found to be carcinogenic.

The principal causes are asbestos (lung and pleural cancer), ionizing radiation (any cancer), and combustion of fossil fuels releasing polycyclic hydrocarbons (skin, lung, bladder cancers). Organic chemicals such as benzene may cause molecular abnormalities associated with the development of myeloid leukaemia.

Infectious agents

Viruses are known to cause cancer in animals. A great deal of time and money has therefore been expended in trying to establish whether they can also cause human cancer. The geographical distribution of a rare malignancy may suggest that it might be caused by, or associated with, an infective agent. For example, a specific type of T-cell leukaemia, seen almost exclusively in the residents from the southern island of Japan and in the West Indies, is caused by infection with the retrovirus, HTLV-1 (human T-cell leukaemia virus) which is endemic in these areas.

Less convincing evidence on causation is available for the association between hepatocellular carcinoma and infection with hepatitis B and C, and Epstein-Barr virus (EBV) with Burkitt's lymphoma and nasopharyngeal carcinoma. Patients with HIV infection or immunosuppression from organ transplantation have an increased incidence of EBV-related lymphoma and herpesvirus 8 associated Kaposi's sarcoma. The incidence of cervical cancer is increasing amongst younger women in association with human papilloma virus infection. Early sexual activity and multiple sexual partners have both been found to be associated with increased risk.

Bacterial infection with Helicobacter pylori is recognized as predisposing to the development of gastric cancer and gastric lymphoma, while Schistosoma japonicum infection predisposes to the development of squamous carcinomas in the bladder.

Drugs

Oestrogens have been implicated in the development of both vaginal and endometrial carcinoma. Alkylating agents and radiotherapy given, for example, for Hodgkin's disease (see later) are themselves associated with an increased incidence of secondary acute myelogenous leukaemia (AML) and bladder cancer. More recently the epipodophyllotoxin, etoposide, has also been shown to be associated with the development of secondary AML.

Cancer Tip Radiation therapy, or radiotherapy, is a common way to treat cervical cancer. Doctors who specialize in treating cancers with radiation are known as radiation oncologists. During radiation therapy, high-energy x-rays are used to kill cancer cells.

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