Tumor viruses, oncogenes, and human cancer.

We review the biology of transforming retroviruses and their relationship to cellular transforming genes (tumor oncogenes). Evidence is discussed for the involvement of a retrovirus in a newly described syndrome, "adult T cell leukemia/lymphoma," which has a high incidence of skin involvement. This virus is related to the animal retroviruses which induce tumors in susceptible hosts after a long latent period. Cellular transforming genes encode proteins which directly change the oncogenic potential of a cell. These genes, which are altered forms of normal cellular genes, have been isolated from a wide variety of human tumors. Viral and cellular transforming genes produce their changes by at least two different mechanisms: abnormally high production of the normal protein encoded by these genes, or normal levels of an altered form of the protein.