[Human cancers and viruses]

There is an increased amount of evidence to suggest that viruses play important roles in the development of certain types of human tumors. These include the hepatitis B virus in hepatocellular carcinoma, human papillomaviruses in cervical cancer, Epstein-Barr virus in Burkitt's lymphoma and nasopharyngeal carcinoma, and human T-lymphotrophic virus in adult T cell leukemia and hairy cell leukemia. These pieces of evidence have accumulated from both clinical and basic studies which have shown that these viruses are involved in some stage of the carcinogenic process. Because of the rapid development of techniques and knowledge of molecular biology, most of the gene structures of these viruses and their products have been identified. These results make it possible to understand more clearly the route of infection and have facilitated the production of vaccines, using DNA-recombinant techniques. A significant decrease in the incidence of these types of cancers is expected through prevention programs conducted throughout the general population against these viruses within 10 to 20 years. These virus-related human cancers also provide us with a good opportunity to understand the basic mechanisms involved in the development of human cancers in general. In the present paper, these points are stressed in addition to describing the recent progress made in the study on virus-related human cancers.