“Cristina Sanchez, a young biologist at Complutense University in Madrid, was studying cell metabolism when she noticed something peculiar. She had been screening brain cancer cells because they grow faster than normal cell lines and thus are useful for research purposes. But the cancer cells died each time they were exposed to tetrahydrocannabinol (THC), the principal psychoactive ingredient of marijuana.

Instead of gaining insight into how cells function, Sanchez had stumbled upon the anti-cancer properties of THC. In 1998, she reported in a European biochemistry journal that THC “induces apoptosis [cell death] in C6 glioma cells,” an aggressive form of brain cancer.

A team of Spanish scientists led by Manuel Guzman conducted the first clinical trial assessing the antitumoral action of THC on human beings. Guzman administered pure THC via a catheter into the tumors of nine hospitalized patients with glioblastoma, who had failed to respond to standard brain-cancer therapies. The results were published in 2006 in theBritish Journal of Pharmacology: THC treatment was associated with significantly reduced tumor cell proliferation in every test subject.

Around the same time, Harvard University scientists ++reported++[http://www.nature.com/bjc/journal/v95/n2/abs/6603236a.html] that THC slows tumor growth in common lung cancer and “significantly reduces the ability of the cancer to spread.” What’s more, like a heat-seeking missile, THC selectively targets and destroys tumor cells while leaving healthy cells unscathed.”  http://www.thedailybeast.com/articles/2012/09/06/marijuana-fights-cancer-and-helps-manage-side-effects-researchers-find.html