Mon May 13, 1:30 PM ET
By Merritt McKinney
NEW YORK (Reuters Health) - Allergies and autoimmune conditions such as lupus and multiple sclerosis may reduce the risk of a particular type of brain tumor, according to the results of a new study.
Researchers are not sure why allergies and autoimmune diseases may protect against brain tumors, but the results suggest that immunological factors may be involved, since both allergies and autoimmune diseases occur when immune system function goes awry.
In most cases, the cause of brain cancer is a mystery. A few hereditary syndromes increase the risk, but they only account for about 5% of all brain tumors. The only proven environmental risk factor is exposure to ionizing radiation.
Recently, several studies have raised the possibility that people with overstimulated immune systems may have a reduced risk of brain cancer. Both allergies and autoimmune diseases result from inappropriate immune reactions. In the case of allergies, the immune system responds to harmless outside substances, while in autoimmune diseases, it launches an attack against the body's own tissue.
To see whether autoimmune disease and allergies offer any protection against brain cancer, a team led by Dr. Alina V. Brenner of the National Cancer Institute (news - web sites) in Bethesda, Maryland, compared 782 people hospitalized with a brain tumor with a "control" group of 799 patients hospitalized for other causes.
Having allergies or an autoimmune illness reduced the risk of some, but not all, brain tumors, Brenner and her colleagues report in the International Journal of Cancer. The risk of a type of brain tumor called glioma was reduced 33% in people with a history of allergies and 51% in those with an autoimmune disease. The risk was lowest in people who had both allergies and autoimmune disease.
The risk of another type of brain cancer, meningioma, was lower in people with an autoimmune disease, but not in those with allergies, the report indicates.
The finding of a reduced risk of glioma in people with a history of allergies or autoimmune diseases is in agreement with several previous studies, according to Brenner. "Given that so little is known about factors that influence the risk of glioma, this finding is particularly exciting," she told Reuters Health.
She cautioned, however, "At this point, it is premature to draw definite conclusions about the underlying basis of the association."
There are several possible explanations for the apparent reduction in risk, according to Brenner. Immune factors that are involved in or predispose people to autoimmunity or allergies might play a role, she said. It is also possible that medications used to treat these conditions could offer some protection. Other factors including some that are not involved with the immune system may also affect the risk, she noted.
"Clearly, this is a promising area of research that warrants further investigation," Brenner said.
SOURCE: International Journal of Cancer 2002;99:252-259.
Copyright © 2002 Reuters Limited