THC, the active ingredient in marijuana, causes brain cancer cells to undergo a process called autophagy in which cells feed upon themselves, according to a study conducted by Guillermo Velasco and colleagues at Complutense University in Spain. Using mice designed to carry human brain cancer tumors, the researchers found that the growth of the tumors shrank when the animals received THC. The study also involved two patients with glioblastoma multiforme, a highly aggressive form of brain cancer. Both patients had been enrolled in a clinical trial designed to test THC's potential as a cancer therapy. The researchers used electron microscopes to analyze brain tissue taken before and after a 26- to 30-day THC treatment regimen. They found that THC eliminated the cancer cells while leaving healthy cells intact. In addition, in what they described as a "novel discovery," the specific signalling route by which the autophagy process unfolds was isolated.

"These results may help to design new cancer therapies based on the use of medicines containing the active principle of marijuana and/or in the activation of autophagy," says Velasco. The findings were published in the April 2009 issue of The Journal of Clinical Investigation.

According to Dr. John S. Yu, co-director of the Comprehensive Brain Tumor Program in the Maxine Dunitz Neurosurgical Institute at Cedars-Sinai Medical Center in Los Angeles, "The findings were not surprising. There have been previous reports to this effect as well. So this is yet another indication that THC has an anti-cancer effect, which means it's certainly worth further study."

Dr. Yu warns cancer patients that they should not consider marijuana a potential cure for cancer and urges that people "not start smoking pot right away as a means of curing their own cancer." However, Dr. Paul Graham Fisher, the Beirne Family director of Neuro-Oncology at Stanford University, says that's precisely what many brain cancer patients are doing. "In fact, 40 percent of brain tumor patients in the U.S. are already using alternative treatments, ranging from herbals to vitamins to marijuana," says Dr. Fisher. "But that actually points out a cautionary tale here, which is that many brain cancer patients are already rolling a joint to treat themselves, but we're not really seeing brain tumors suddenly going away as a result, which we clearly would have noticed if it had that effect."

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