A review of human carcinogens--Part B: biological agents.

In February, 2009, 36 scientists from 16 countries met at the International Agency for Research on Cancer (IARC) to reassess the carcinogenicity of the biological agents classifi ed as “carcinogenic to humans” (Group 1) and to identify additional tumour sites and mechanisms of carcinogenesis (tables 1 and 2). These assessments will be published as part B of Volume 100 of the IARC Monographs. Hepatitis B virus (HBV) and hepatitis C virus (HCV) infect, res pectively, over 300 million and 170 million people worldwide, mainly in Asia and Africa. Chronic infection with these viruses is known to cause hepatocellular carcinoma. Suffi cient evidence is available to conclude that chronic infection with HCV can also cause non-Hodgkin lymphoma, especially B-cell lymphoma. In an inter vention study, patients with HCV infection and splenic lymphoma who were given the antiviral agent, interferon, showed regression of the lymphoma. Epstein–Barr virus (EBV) infects almost everyone and causes several types of cancer, including nasopharyngeal carcinoma, one of the most common cancers in southeastern Asia, and Burkitt’s lymphoma in children in Africa. New evidence points to a role for EBV in 5–10% of gastric carcinomas worldwide. EBV-positive gastric carcinoma develops early in life and has distinct histopathology, therefore it might belong to a separate clinical entity. In this subset of gastric tumours, presence of the viral genome in a monoclonal form and expression of EBV-transforming proteins are strong evidence for the involvement of EBV. Data from 22 cohort studies and 80 case–control studies show an association between Kaposi’s sarcoma herpes virus (KSHV) and Kaposi’s sarcoma, with relative risks higher than 10. Most studies are of transplant recipients and people infected with HIV-1. In both patients who are and are not infected with HIV-1, risk of Kaposi’s sarcoma increases relative to increasing titre of antibodies directed against KSHV, which are markers of the viral load. Evidence is suffi cient to show that KSHV causes primary eff usion lymphoma, a rare subgroup of B-cell non-Hodgkin lymphoma. Mechanistic data support an oncogenic role for KSHV in Kaposi’s sarcoma and in primary eff usion lymphoma—in individuals who are immunocompromised and in those apparently immunocompetent. KSHV is also associated with multicentric Castleman’s disease. Individuals who are infected with HIV-1 have a high risk of cancer. HIV-1 infection, mainly through immunosuppression, leads to increased replication of oncogenic viruses such as EBV and KSHV. Although antiretroviral therapy lowers the risk of many cancers associated with HIV-1, risks remain high. Cervical cancer is caused by types of human papillomavirus (HPV) that belong to a few phylogenetically related “high-risk” species (alpha-5, 6, 7, 9, 11) of the mucosotropic alpha genus. The types found most frequently in cervical cancer (HPV-16, 18, 31, 33, 35, 45, 52, 58) and four types less constantly found (HPV-39, 51, 56, 59) were classifi ed in