http://science.iowamedicalmarijuana.org/pdfs/cancer/Luca%20et%20al%202009%2019539619.pdf Link 1 http://www.ncbi.nlm.nih.gov/pubmed/19108691 Link 2 gan.sagepub.com/content/early/2012/11/08/1947601912466556.abstract Link 3 http://www.biomedcentral.com/1741-7015/2/34 Link 4 So no epidemiological association and three other studies which show inhibiting and apoptotic effects on Kaposi's sarcoma cell lines. The study you were talking about is this one: http://europepmc.org/abstract/MED/17671191/reload=0;jsessionid=pYZgy309OXE82g2c71qn.16 Link 5 Where they studied just one specific cell line and only the effect of low levels of THC. If you take into account all of the studies and the fact cannabis is much more than just THC, the study you posted becomes quite meaningless.