The current debate over medical marijuana hinges on its use as pain medication. But an extract of the plant could one day form the basis of cancer treatments. New findings indicate that Cannabis extracts can shrink brain tumors by blocking the growth of blood vessels that nourish them.

Manuel Guzman of Complutense University in Spain and his colleagues tested extracts of marijuana known as delta-9-tetrahydrocannabinols in 30 mice that had brain tumors. The researchers analyzed the animals' DNA and identified 267 genes associated with blood vessel growth, or angiogenesis. The cannabinoids inhibited the expression of several genes critical to angiogenesis known as the VEGF (vascular endothelial growth factor) pathway. Blockade of the VEGF pathway constitutes one of the most promising antitumoral approaches currently available, Guzman says. The cannabinoids work by increasing the potency of a fat molecule known as ceramide, the team posits. Increased ceramide activity, in turn, inhibits cells that would normally produce VEGF and encourage blood vessel growth.

The scientists also tested the therapy on tumors taken from two patients who had not responded to conventional therapy for their glioblastoma, a deadly form of brain cancer. After the cannabinoid injections, both tumors exhibited decreased VEGF levels. Writing in the current issue of the journal Cancer Research, the team notes, however, that a combination of therapies will most likely be required to obtain significant clinical results.