the Cancer.gov website actually has a fair and unbiased section on cannabis although I have only skimmed through it. http://www.cancer.gov/cancertopics/pdq/cam/cannabis/healthprofessional/page1
An <i>in vitro</i> study of the effect of CBD on programmed cell death in breast cancer cell lines found that CBD induced programmed cell death, independent of the CB1, CB2, or vanilloid receptors. CBD inhibited the survival of both estrogen receptor–positive and estrogen receptor–negative breast cancercell lines, inducing apoptosis in a concentration-dependent manner while having little effect on nontumorigenic, mammary cells.[19] ...Another investigation into the antitumor effects of CBD examined the role of intercellular adhesion molecule-1 (ICAM-1).[12] ICAM-1 expression has been reported to be negatively correlated with cancermetastasis. In lung cancer cell lines, CBD upregulated ICAM-1, leading to decreased cancer cell invasiveness.