Cancer is characterized by an abnormal growth of cells. There are more than 100 types of cancer, including breast cancer, skin cancer, lung cancer, colon cancer, prostate cancer, and lymphoma. Cancer symptoms vary widely based on the type of cancer. Cancer treatment includes chemotherapy, radiation, and surgery, but cannabis is increasingly becoming a valid treatment option for those who suffer from this disease.

Most cancers form a tumor but some, like leukemia, do not. Cancer affects people at all ages with the risk for most types increasing with age. The National Cancer Institute estimates that nearly 12 million Americans with a history of cancer were alive in January 2008. Some of these individuals were cancer free, while others still had evidence of cancer and may have been undergoing treatment.

Cancers are caused by abnormalities in the genetic material of the transformed cells. These abnormalities may be due to the effects of carcinogens, such as tobacco smoke, radiation, chemicals, or infectious agents. Other cancer-promoting genetic abnormalities may randomly occur through errors in DNA replication, or are inherited, and thus present in all cells from birth.

Most cancers can be treated and some cured, depending on the specific type, location, and stage. Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for different varieties of cancer. There has been significant progress in the development of targeted therapy drugs that act specifically on detectable molecular abnormalities in certain tumors, and which minimize damage to normal cells. The prognosis of cancer patients is most influenced by the type of cancer, as well as the stage, or extent of the disease.

At the University of Rostock, a study entitled "Antitumorigenic Effects of Cannabinoids Beyond Apoptosis" concluded, "During past years the antitumorigenic effects of cannabinoids have emerged as an exciting field in cancer research. Apart from their proapoptotic and antiproliferative action, recent research has shown that cannabinoids may likewise affect tumor cell angiogenesis, migration, invasion, adhesion and metastasation."

Researchers at the Complutense University in Spain found, "We showed that autophagy is upstream of apoptosis in cannabinoid-induced human and mouse cancer cell death and that activation of this pathway was necessary for the antitumor action of cannabinoids in vivo. These findings describe a mechanism by which THC can promote the autophagic death of human and mouse cancer cells and provide evidence that cannabinoid administration may be an effective therapeutic strategy for targeting human cancers."