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But the findings shouldn't send patients rushing to buy pot: the levels used in the research appear to be too high to obtain through smoking. And there's no sign yet that the approach works in laboratory animals, let alone people.
Still, the finding does suggest that more than one compound in marijuana might boost cancer treatment, said study author Sean McAllister, an associate scientist at California Pacific Medical Center Research Institute in San Francisco. "Combination therapies might be more appropriate," McAllister said.
Researchers have long studied the compounds in marijuana known as cannabinoids, which are thought to hold possible health benefits. One, known as THC, is well known for its role in making people high when they smoke or eat pot. Researchers have been testing it as a treatment for the brain tumors known as glioblastomas.
In the new study, researchers tested THC and cannabidiol, another compound from marijuana, on brain cancer cells. The findings appear in the January issue of Molecular Cancer Therapeutics.
The study authors found that the combination treatment seemed to work better at killing the cancerous cells and preventing them from growing back.
About 9,000 people in the United States develop glioblastomas each year, said Dr. Paul Graham Fisher, chief of the Division of Child Neurology at Stanford University and Lucile Packard Children's Hospital. The most famous patient was the late U.S. Senator Ted Kennedy.
The prognosis for people with the condition is grim because tumors spread throughout the brain. It can be impossible for treatments to remove the entire tumor, Fisher said.
"No matter what you do, this tumor has a larger border than you ever think," he said. "We know there are microscopic satellites all throughout one side of the brain and pretty soon in the other side of the brain. The only thing that will fix this disease is something that provides a more blanket approach."
Instead of targeting the tumors itself, he explained, treatments need to do something like disrupt the pathways that cancer cells use to communicate.
In the big picture, "you're seeing a lot more thinking outside the box about trying to treat glioblastoma," he said. "I think in the next 10 to 15 years we're going to start seeing progress forward."
For now, he said, there's no evidence that marijuana is good or bad for glioblastoma tumors.
Back in the laboratory, McAllister said the next step is to test the combination treatment on laboratory animals and then on people. The treatment may be given to people directly through the brain, which could be expensive. But the compounds themselves may not be expensive, McAllister said.
As for the idea of getting the same effect through a couple of marijuana joints, he had this to say: "It's unlikely that you could reach effective concentrations by smoking the plant."
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SOURCES: Sean McAllister, Ph.D., associate scientist, California Pacific Medical Center Research Institute, San Francisco; Paul Graham Fisher, M.D., chief, division of child neurology, Stanford University and Lucile Packard Children's Hospital, Palo Alto, Calif.; January 2010, Molecular Cancer Therapeutics
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