ST. LOUIS (Reuters) - Neurosurgeons using lasers to treat brain cancer have discovered the technique breaks down the blood-brain barrier, a finding that could potentially lead to new treatment options for patients diagnosed with the deadly disease.

The blood-brain barrier is a sort of natural "security system" that filters out drugs and other substances in blood so they can't reach the brain.

"We were able to show that this blood-brain barrier is broken down for about 4 weeks after you do this laser therapy," said Dr. Eric Leuthardt, a professor of neurosurgery at Washington University in St. Louis.

"So not only are you killing the tumor, you are actually opening up a window of opportunity to deliver various drugs and chemicals and therapies that could otherwise not get there," he added.

Currently the research is in a second round clinical trial. The blood-brain barrier shields the brain from harmful toxins but also blocks potentially helpful drugs, such as chemotherapy.

The laser technology, which was approved by the Food and Drug Administration in 2009 as a surgical tool that can be used to treat brain tumors, involves a small laser tipped probe that heats up and kills tumors from the inside out.

As part of the trial, following the laser therapy, patients are dosed with doxorubicin, a powerful chemotherapy drug known as one of the least likely to get through the blood-brain barrier.

"Kind of makes you smile when they say you are a good candidate for something new," said Kathy Smith, a participant in the trial who has been battling cancer since 2009.

Initially diagnosed with ovarian cancer, Smith is currently being treated for recurrent glioblastoma, one of the most difficult forms of cancer to treat. Most patients diagnosed with these types of brain tumors survive just 15 months, according to the American Cancer Society.

The trial is still ongoing but Leuthardt says the initial results are promising.

"What's interesting is that the blood-brain barrier is a two way street," said Leuthardt. "By breaking it down you can get things into the brain, but also by breaking it down now things can go from your brain out into your circulation, to your peripheral system which includes your immune system."

Leuthardt is using drugs to "amplify the immune system to fight the cancer" in combination with laser therapy.

Utilizing the "two way street" comes with risks as it breaks down the brain's natural defenses, but for patients with brain cancer, says Leuthardt, any treatment that could potentially extend their lives is a risk worth taking.

Leuthardt says that even if the current trial has negative results, the blood-brain barrier discovery could potentially open up more treatment options in the future.

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Kathy Smith is still battling cancer. She says she knows it's an uphill battle, but she says every day leads to new discoveries and new hope.

The researchers are hoping to publish their findings later this year.