This is information found on The National Cancer Institute website (cancer.gov):

Antitumor activity

• Studies in mice and rats have shown that cannabinoids may inhibit tumor growth by causing cell death, blocking cell growth, and blocking the development of blood vessels needed by tumors to grow.  Laboratory and  animal studies have shown that cannabinoids may be able to kill cancer cells while protecting normal cells.
  
  


• A study in mice showed that cannabinoids may protect against inflammation of the  colon and may have potential in reducing the risk of  colon cancer , and possibly in its treatment.
  
  


• A laboratory study of delta-9-THC in  hepatocellular carcinoma (liver cancer) cells showed that it damaged or killed the cancer cells. The same study of delta-9-THC in  mouse models of liver cancer showed that it had  antitumor effects. Delta-9-THC has been shown to cause these effects by acting on molecules that may also be found in  non-small cell lung cancer cells and  breast cancer cells.
  
  


• A laboratory study of cannabidiol in  estrogen receptor positive and  estrogen receptor negative breast cancer cells showed that it caused cancer cell death while having little effect on normal  breast cells.