“Cannabis has been shown to kill cancer cells in the laboratory” http://www.cancer.gov/about-cancer/treatment/cam/patient/cannabis-pdq
“A review of bladder cancer rates in Cannabis users and non-users was done in over 84,000 men who took part in the California Men’s Health Study. Over 16 years of follow-up and adjusting for age, race/ethnic group and body mass index (BMI), rates of bladder cancer were found to be 45% lower in Cannabis users than in men who did not report Cannabis use.” http://www.cancer.gov/about-cancer/treatment/cam/patient/cannabis-pdq#section/_3