Human leukemia viruses? RNA tumor viruses, human malignancies, and concepts of viral carcinogenesis.

For an elucidation of the definitive role of retroviruses in human carcinogenesis the expression of viral parameters during the course of induced malignant diseases has to be studied. For obvious reasons these studies can only be carried out in animal systems. On the basis of such studies the human data will have to be reevaluated as to what the function of the viruses for the course of malignant diseases might be. In addition, with the development of more sensitive techniques for the detection of viral footprints, such as genetic engineering, the significance of retroviruses with regard to human neoplasms will have to be reevaluated. Finally, in view of the well-known role of many factors in carcinogenesis and the probable multifactorial etiology of human cancer, 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