Breast cancer primarily affects women, but men also have about a .1% chance of developing the disease (U.S. Breast Cancer). Many forms of the disease are highly aggressive, and there is a great need for new treatments.
A 2010 study by Dr. Manuel Guzmán's team illustrated how THC combated a specific form of breast cancer; it also examined the nature of cannabinoid receptor expression in different mammary tissues (Caffarel et al.). Normal, non-transformed tissue had no significant CB1 or CB2 expression, while breast cancer cells had low CB1 expression and high CB2 expression. ErbB2- positive breast cancer had especially high levels of CB2 receptors. The ErbB2 tyrosine kinase receptor is a member of the EGF receptor family, and its overexpression in breast cancer cells is associated with very aggressive, highly invasive, highly proliferative, and poorly differentiated cancers.
In mice, THC strongly reduced tumor growth. It also decreased the number of tumors the animals generated throughout treatment. THC-treated animals never developed more than three tumors, whereas 41% of untreated animals developed four or more tumors. The synthetic CB2 agonist JWH-133 was also effective.