The viral etiology of cancer: a realistic approach.

The etiology of cancer resembles that of many other diseases in that multiple factors may be required. Because of this, the role or viruses in the etiology of human cancers is especially difficult to assess. When animal tumor systems were used as models, the roles of various predisposing characteristics in virus oncogenesis were elucidated. Extrapolation of these findings to the human diseases suggests the importance of genetics, age, hormones, immune competence, and stress in determining susceptibility to tumor development in individuals infected with an oncogenic virus. The importance of cofactors in induction of those human tumors most strongly associated with virus infection, including Burkitt's lymphoma, nasopharyngeal carcinoma, cerviccal carcinoma, acute myelogenous leukemia, and breast cancer, is reviewed. Understanding of the role of these cofactors in virus carcinogenesis may lead to disease prevention through elimination of one or more of the cofactors.