Infections

16% of the worldwide incidence of cancer is due to infection. For developed countries, the proportion is 9%, and for developing countries, 21%. Human papillomavirus (HPV) of any type accounts for 82% of cervical cancers in developed countries and 91% in developing countries. The human papillomaviruses occur in 70 different types. The strongest evidence for carcinogeneity is for HPV types 16 and 18. 81% of cases of liver cancer are attributable to chronic infection with hepatitis B or hepatitis C.

Strong evidence supports a causal relationship between chronic infection with the bacterium Helicobacter pylori and the development of gastric adenocarcinoma, and there is some evidence for gastric lymphoma. 60% of cases of gastric cancer in developed countries, and 53% in developing countries, may be attributable to Helicobacter pylori.

Epstein-Barr virus may account for up to 60% of Hodgkin's disease in developed countries, and 80% in developing countries. The virus accounts for over 90% of cases of Burkitt's lymphoma in sub-Saharan Africa, just over 80% in north Africa and the Middle East, just under 50% in Latin America and the Caribbean, and less than a quarter of cases elsewhere. There is greater uncertainty about the role of the virus in other types of non-Hodgkin's lymphoma and nasopharyngeal carcinoma.

Other infections considered to be carcinogenic include: ♦ Schistosomiasis haematobium and bladder cancer (attributable proportion in developing countries 8%, in developed countries 0%).

♦ Human T-cell lymphotrophic virus and acute T-cell leukaemia/ lymphoma (attributable proportion worldwide 1%).

♦ HIV and non-Hodgkin's lymphomas.

♦ Opisthorchis viverrini and Clonorchis sinenis and cholangio-carcinoma.

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