Aetiology of cancer in Asia.

Cancer has become the leading cause of death in many Asian countries. There is an increasing trend in breast, prostate and colon cancers, which are considered as typical of economically developed countries. Although breast and prostate cancer rates are still lower than in western countries, they are particularly rapidly increasing. In this paper, we review recently published literature to identify important etiologic factors affecting the cancer risk in Asian populations. Infectious agents such as Helicobacter pylori, hepatitis B and C viruses, and human papillomavirus were shown to be associated with elevated risks of stomach, liver and cervical cancer, respectively. Tobacco smoking was shown to be significantly associated with higher lung cancer risk and moderately increased all cancer risk. Excessive alcohol drinking appeared to increase the risk of colorectal cancer in Japanese and breast cancer in the Korean population. Betel nut chewing was associated with higher risk of oral and esophageal cancer. In terms of diet, various studies have demonstrated that high caloric and fat intake was associated with breast cancer risk, salted food intake with stomach cancer, aflatoxin B1 with liver cancer, and low fruits and vegetables intake with breast and lung cancer. Environmental exposure to indoor and outdoor air pollution, arsenic, radon, asbestos and second hand smoke was shown to increase the lung cancer risk. Reproductive factors such as late age at first childbirth, early menarche, late menopause, oral contraceptive intake, and short duration of lifetime lactation were shown to be associated with breast and/or colorectal cancer. Cancer has clearly become an emerging health threat in Asia and cancer control programs should be actively implemented and evaluated in this region. Various strategies for cancer control have been developed in some Asian countries, including the set-up of national cancer registries, cancer screening programs, education programs for health behavior change, eradication of Helicobacter pylori and vaccination for hepatitis B and C viruses, and human papilloma virus high risk forms. However, more attention should also be paid to low- and medium-resource Asian countries where cancer incidence rates are high, but neither intensive research on cancer for planning effective cancer control programs, nor easy implementation of such programs are available, due to limited financial resources.