“scientists reported that THC and other cannabinoids such as CBD (cannabidiol) slows growth and/or causes death of certain types of cancer cells growing in laboratory dishes. Some animal studies suggest certain cannabinoids may slow growth and reduce spread of some forms of cancer”

http://www.cancer.org/Treatment/TreatmentsandSideEffects/
ComplementaryandAlternativeMedicine/HerbsVitaminsandMinerals/marijuana