Major avoidable risk factors of cancer.

With an aim of promoting primary prevention of cancer, major avoidable risk factors as well as protective factors of cancer are reviewed based on previous epidemiological studies. Among various risk factors of cancer, tobacco is the most important avoidable risk factor for cancers of the oral cavity, larynx, lung, pharynx, esophagus, stomach, liver, pancreas, kidney (pelvis), ureter, bladder, and cervix. Tobacco accounts for some 20-30% of all sites of cancer. Betel quid and tobacco chewing is an important risk factor for cancer of the oro-pharynx in some parts of South-East Asia. Diet also plays an important role in the etiology of cancer, but its relation to cancer is complicated. An excess or insufficient intake of some food components elevates risk of cancer of several sites. Eating habits, available foods, methods of food processing may vary from country to country. Infection of oncogenic viruses (especially, HBV, HVC, HPVs) is an important avoidable risk factor of cancer where liver cancer and cervical cancer are common. Infection of Helicobacter pylori could also be an important risk factor of stomach cancer. Attributable risks of other avoidable risk factors, such as occupation, environmental pollution, sun light, radiation, food additives, pesticides, drugs, etc. are relatively small compared to those of tobacco, diet and infection. Exercise and stress are also manageable risk factor of cancer.