Antihistamine Use Tied to Brain Tumors

April 4, 2006 (Washington) -- Taking antihistamines may raise the risk of developing certain types of brain cancer, a new study shows.

"We want to stress that this is preliminary data and that antihistamines do not cause brain cancer," says researcher Michael Scheurer, PhD, of the University of Texas M.D. Anderson Center in Houston.

Given how many people take antihistamines to relieve sneezing, itching, dry mouth, and other allergy symptoms, "many more people would have brain tumors if they did," he tells WebMD.

Reporting at the annual meeting of the American Association for Cancer Research, Scheurer says he believes this is the first study to look at the potential effects of antihistamines on the development of brain tumors in adults.

That said, a relationship between the two makes sense.

The reason: About a half dozen previous studies have suggested that people with allergies or asthma have a lower risk of the most deadly type of brain tumor, called glioblastoma.

"Allergies and asthma may produce enough inflammation in the brain to keep immune system cells active and working to prevent cancer," Scheurer says.

Since people take antihistamines to counter allergy's effects, the researchers wanted to see if the drugs also counter allergy's protective effects.

Gliobastomas are the most common of brain cancers, accounting for 50% to 60% of the 17,000 new brain cancers each year in the U.S. They're also the most potent, taking the lives of another 17,000 men and women, Scheurer says. "But very little is known about their cause."

Somewhat surprisingly, antihistamine use did not affect the risk of developing glioblastomas one way or another.

But the allergy drugs were associated with increased risk of other types of brain tumors. Specifically, people who used the medications regularly were 2.8 times more likely to develop lesser-grade anaplastic astrocytoma brain tumors and 86% more likely to develop low-grade glioma brain tumors than people who didn't take the drugs.

That's not to say the findings are trivial, however: Even low-risk brain tumors are often deadly, Scheurer says.

The study also confirmed that people with allergies or asthma are less likely to develop brain tumors. They were 36% less likely to have glioblastoma, 53% less likely to have anaplastic astrocytomas, and 37% less likely to have low-grade gliomas than people without the conditions.

Results also lined up with previous reports that both anti-inflammatory drugs and chickenpox confer protection against glioblastoma, Scheurer says.

"Once you have the chickenpox, the virus that causes it stays with you forever, lying dormant in the brain," he says. "It's hypothesized that the latent virus causes low levels of inflammation. And inflammation has been linked to the development of a variety of cancers."

To arrive at their findings, the researchers combined data from two studies in which participants were asked about their use of antihistamines and anti-inflammatory drugs. A total of 610 people with brain tumors and 831 people without cancer were included in the final analysis.

John D. Potter, PhD, senior vice president of the Fred Hutchinson Cancer Research Center in Seattle and moderator of a news conference to discuss the findings, stresses that people who take antihistamines should not panic or stop taking the drugs when needed.

"This study adds to information we have showing that inflammatory processes are important in the development of cancer. It does not tell us that drugs like antihistamines cause cancer," he tells WebMD.

"It's a mechanism we should be exploring, not a risk factor we should be modifying," Potter says.

Scheurer agrees. One hypothesis he hopes to explore is to determine whether antihistamines work in concert with as-yet undetermined genetic factors to raise brain cancer risk.

"It could be that some people are predisposed to develop the tumors and antihistamine use is just speeding it up," he says. "That's a topic for future research."

SOURCES: American Association of Cancer Research annual meeting, Washington, April 1-6, 2006. Michael Scheurer, PhD, University of Texas M.D. Anderson Center, Houston. John D. Potter, PhD, senior vice president, Fred Hutchinson Cancer Research Center, Seattle.

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