Viruses and cancer risk in man.

The present state of tumor virus research in man is analysed in order to evaluate the cancer risk by viruses in man. For most of the viruses isolated from human tumorous or normal tissues and similar to oncogenic viruses of animals the participation as causative agent in the multifactorial process of cancer induction, promotion and realization in man is not yet established. This holds true for DNA viruses (paillomaviruses, SV 40-related viruses, Herpesvirus 2, hepatitis B virus) as well as for the retroviruses. There are, however, data which give circumstantial evidence for the association of members of these groups of viruses with certain types of human tumors. The foremost candidate as human tumor virus is the Epstein-Barr virus--an essential causative factor for Burkitt's lymphoma and nasopharyngeal carcinomas.