Epidemiology of Cancer in Women

Abstract

Risk factors for cancer in women can be considered under two major headings: those exposures and forms of cancer similar to men and those exposures and forms of cancer unique to women. In many countries, the rates of lung cancer in women are increasing substantially and seem set to overtake breast cancer as the most common form of cancer in women. These changes are due to the effect of the cigarette smoking habit which became common in women much later than in men. Indeed, the high levels of smoking current in young women constitute an important hazard not only for future cancer risks but for several other important causes of death. The effect of the main carcinogens appears to be similar in men and women with the major difference in the observed effect due to differences in the exposure levels (‘dose’) to either gender group. There are now somewhat over 350 studies which have investigated the association with cancer risk and consumption of fruits and vegetables. There is strong and consistent evidence that increased consumption levels are associated with reduced risks of many varied common forms of cancer. Some of the most common forms of cancer in women arise in either the breast or the female genital tract and it is strongly suspected that the majority of these tumours have an etiology which is strongly related to female hormones. Although the breast is the most common form of cancer in women in most western countries and has been the subject of a large number of epidemiological studies, an understanding of the etiology of this disease remains elusive and preventable causes remain to be identified. Exogenous as well as endogenous hormones appear to have a role in cancer risk in women: oral contraceptives seem to increase the risk of breast cancer in young women (up to about the age of 38) but appear to be protective against ovarian and endometrial cancer. The use of estrogens as hormonal replacement therapy (HRT) appears to increase the risk of endometrial cancer and the association with breast cancer risk still cannot be discounted after many conflicting studies. The addition of progestins appears to reduce the effect of estrogens on endometrial cancer. Within our current knowledge of the epidemiology of cancer in women, the most important preventive strategies would appear to be the prevention of cigarette smoking and increased dietary intakes of fruits and vegetables. In the future, vaccination against human papilloma virus could play a significant role in reducing the incidence of cancer of the cervix and it seems worthwhile at the present moment to undertake randomized trials of tamoxifen intervention in well women to reduce the risk of breast cancer. It may be possible and worthwhile in the future to instigate trials of tamoxifen and hormonal replacement therapy including progestins in breast cancer prevention.