“Lewis lung adenocarcinoma growth was retarded by the oral administration of delta9-tetrahydrocannabinol (delta9-THC), delta8-tetrahydrocannabinol (delta8-THC), and cannabinol (CBN), but not cannabidiol (CBD)… CBD was active only in high concentrations.”

http://www.ncbi.nlm.nih.gov/pubmed/1159836