Retroviruses and human cancer.

Retroviruses have long been associated with cancer in many species. Human T cell leukaemia virus type I causes adult T cell leukaemia. Human immunodeficiency virus infection is associated with lymphoma and Kaposi sarcoma, but oncogenesis is largely secondary to its effect on the immune system. The incidence of Kaposi sarcoma varies greatly in different social groups with AIDS, being most frequent among male homosexuals; an unknown, sexually transmissible agent may be responsible. Human endogenous retroviral genomes are linked with myeloproliferative disease. Finally, the risk is discussed that cancer could be a side-effect of the use of retroviral vectors in human gene therapy.