Silverman's rather magnificent article on XMRV in prostate cancer puts forward some possible mechanisms for causing cancer. http://www.nature.com/nrurol/journal/v7/n7/full/nrurol.2010.77.html "XMRV does not possess direct transforming activity, at least not as measured by focus formation in fibroblast and epithelial cell lines.59 However, XMRV did rarely induce transformation of a rat fibroblast line, which suggests an indirect mode of action. In one instance, an XMRV-transformed focus even produced virus with a high level of transforming activity, suggesting a recombination event possibly involving acquisition of a host oncogene. Another two transformation events might have been the result of insertional activation of cellular oncogenes. Presumably, in order for XMRV to contribute to prostate cancer by this mechanism, active viral replication would be necessary with multiple integration events, until an integration occurred in a cellular oncogene" Basically he's putting forth some of the possible ways XMRV could be cause cancer in the prostate even though it can't directly turn on the cellular genes that cause the cell to turn cancerous: E.G. active viral replication causes the virus to insert (integrate it's RNA) into different sites on the host cell cancer gene (oncogene)-- meaning it isn''t built to directly upregulate or the oncogene but could do so as a result of screwing things up cumulatively so to speak. He also mentions chronic inflammation "microenvironment" in local cells or adjacent cells. Worth wading through in moments when my fog lifts.