Allergic to cancer

Overactive immune systems may protect against certain types of brain tumor

Hay fever, dog, peanut and other allergies may protect sufferers from certain types of brain tumors, a new study suggests.

In surveys of hospital patients, individuals with glioma — a common form of brain and spinal cancer — were less likely than cancer-free individuals to report having allergies, University of Illinois at Chicago researchers report online February 7 in Cancer Epidemiology, Biomarkers & Prevention.

Several teams had previously explored the link between allergies and glioma, says UIC epidemiologist Bridget McCarthy, who led the study. Her team set out to confirm these results, cobbling together a wide list of variables. The researchers quizzed about 1,000 hospital patients with or without cancer about their allergy histories. Of the 344 patients with high-grade glioma, about 35 percent reported having been diagnosed with one or more allergies in their lifetimes, compared with about 46 percent of the 612 cancer-free respondents. About 10 percent of high-grade tumor patients had three or more allergy diagnoses, as opposed to 19 percent of the controls. “The more allergies you have, the more protected you were,” McCarthy says.

Glioma isn’t the first cancer to be negatively correlated with common allergies, says Michael Scheurer, an epidemiologist at Baylor College of Medicine in Houston. Allergy-prone people may fight off colorectal and pancreatic cancer, and even childhood leukemia, better than sniffles-free people, according to some studies. At the other end of the spectrum, allergies that cause asthma may spur lung tumors.

Just why these links exist isn’t clear. Allergy sufferers mount heightened immune responses to some foreign or dangerous cells and chemicals, says Scheurer, who was not involved in the study. And cancer cells are certainly dangerous — human immune systems naturally seek them out. The immune systems in people with allergies may just do it better. “They have an overactive immune system, and maybe that’s been protecting them from the development of tumors,” he says.

In December, Scheurer and his colleagues reported finding a link between risk for one type of glioma and use of the antihistamine drugs like diphenhydramine — the active ingredient in Benadryl. The Chicago team did not find such a link.

Scheurer says Benadryl users shouldn’t worry. “Brain tumors are very, very rare tumors, and a lot of people take antihistamines.” He suspects that in a small set of individuals with a genetic predisposition to brain cancer, antihistamines may slow down the immune response, giving cancer cells an opening. 

These sorts of studies can easily produce varying results simply because there are so few participants, Scheurer adds. His colleague Melissa Bondy at the University of Texas M.D. Anderson Cancer Center in Houston has launched an effort to conduct similar surveys of 6,000 glioma patients and a comparison group without the disease. Both McCarthy and Scheurer hope that such efforts will give researchers a better look at what makes brain tumors grow.

Glioma and brain tumors in general are rare, Scheurer says, but devastating. Few patients with high-grade glioma survive longer than five years. So there’s a big need to develop safe and effective treatments. “There’s a strong community of researchers who are interested in brain tumors,” he says. “And we don’t give up.”

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