[Factors involved in the development of human tumors using the Epstein-Barr virus as an example (author's transl)].

Several viruses induce tumors in animals under experimental or natural conditions. It is likely therefore that some human malignancies are also caused by viruses. Proof of this hypothesis can be provided only by indirect evidence based on the following criteria: (1) detection of viral antigens or viral genetic information in a given tumor; (2) transformation of normal human cells by the virus in tissue culture; (3) induction of tumors in animals by the virus; and (4) demonstration of enhanced titers of antibodies to the virus in patients bearing the tumor. These criteria have been fulfilled to support a causal relationship of the Epstein-Barr virus (EBV) in Burkitt's lymphoma and nasopharyngeal carcinoma. It is clear, however, that factors of a genetic, immunologic or environmental nature must play an additional role because EBV, the cause of infectious mononucleosis, is widely disseminated yet development of the tumors is a rare event.