RNA-tumorviruses, oncogenes, and their possible role in human carcinogenesis.

The detection and characterization of oncogenes via RNA tumor viruses (or retroviruses) and the recognition of their location at breakpoints of chromosomal translocations which are frequently found in certain human neoplasms has promoted present understanding of molecular mechanisms underlying carcinogenesis. Oncogenes are cellular genes which can be transduced by RNA tumorviruses and induce malignant transformation under experimental conditions in vivo and in vitro. A role of retroviruses in human leukemogenesis is suggested by epidemiological observations and by the isolation of such viruses from several human T-cell leukemias and lymphomas (human T-cell leukemia/lymphoma virus or HTLV) as well as by biochemical association of retroviral markers with human leukemias. A role of HTLV has been suggested also in a human immune deficiency syndrome (AIDS). In view of the well known role of many factors in carcinogenesis the concept of carcinogenesis as a multistep process as well as the concept of cocarcinogenesis and the role of cofactors other than viruses, such as radiation and chemicals, aging, hormones, graft vs host reaction, environmental factors etc., will have to be carefully considered.