Possible retroviral etiology of human breast cancer.

Since the discovery in the early 1980s that retroviruses are pathogenic to man, the mouse mammary tumor viruses (MMTVs) received great attention. Studies of MMTVs allowed considerable insights into the mechanisms at work in breast tumorigenesis. MMTVs are essentially insertional mutagenes. Numerous oncogenes have been found altered by MMTVs, either specific for MMTVs or not. However, despite considerable attempts, the involvement of MMTVs in human breast cancer remains questionable. Yet a retroviral etiology of human breast cancer cannot be discarded since retroviruses are good candidates to play a role in diseases which, like human breast cancer, appear either as sporadic or inherited. Due to their replication cycle, retroviruses can be propagated not only as infectious agents able to freely infect host cells, but also as cellular genes which can be passed on to progeny. It is suggested here to search for a new human retrovirus in sporadic breast cancer, using the techniques which led to the isolation of human T-cell leukemia virus-1 (HTLV-1). Indeed, finding an infectious retrovirus in sporadic cases could lead, via the c-DNA probes derived from it, to testing the hypothesis that the inherited form of human breast cancer may result from the action of retroviral genes integrated in the germ line.