Viruses and Human Cancer

THE contention that viruses may cause cancer in man rests mainly on analogy with observations in other species, particularly laboratory animals.1,2 However, even if tumor viruses were known not to cause human cancer they would be a suitable starting place for the study of genetic mechanisms in neoplasia. Oncogenic viruses have from seven to 50 genes, only a few of which are required to confer malignancy on an infected cell. These viruses obviously represent a more promising place to search for oncogenic genes than mammalian cells, which contain two million genes or more.3,4Approaches to Cancer VirusesViruses probably evolved . . .