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.