Viruses in Carcinogenesis

SUMMARY

This article reviews the role of viruses in cancer. Oncogenic viruses may contain either ribonucleic acid (RNA) or deoxyribonucleic acid (DNA). The small DNA viruses, polyoma virus and SV40, are best known in terms of genetics and molecular biology. Cell transformation by these viruses includes two steps: first, the integration of the viral DNA in the cellular DNA; and secondly, the expression of viral transforming functions. If integration fails, the cells undergo abortive transformation and then return to normality. In the transformed cell only some of the viral genes are transcribed into messenger RNA, and this accounts for the survival of the cells. The RNA viruses are less well known. They produce either leukemias with very low efficiency or (sometimes) sarcomas with a high efficiency. The sarcoma viruses often have complex biology.

An extensive search is going on for viruses as possible agents of human cancer. The most interesting virus is the one found in the Burkitt's lymphoma cells and, in all likelihood, the agent of infectious mononucleosis. The search for human cancer viruses is beset by great difficulties, both methodological and conceptual.