” Here, we show that Delta(9)-tetrahydrocannabinol (THC), through activation of CB(2) cannabinoid receptors, reduces human breast cancer cell proliferation by blocking the progression of the cell cycle and by inducing apoptosis… these data might set the bases for a cannabinoid therapy for the management of breast cancer.”

http://www.ncbi.nlm.nih.gov/pubmed/16818634