The findings by a Cornell University team comprising Paul Sherman, Erica Holland and Janet S. Sherman suggest that allergy symptoms may protect against these conditions by expelling foreign particles, which may be carcinogenic or carry absorbed carcinogens, from organs likely to come in with contact them. Besides, allergies serve as early warning devices that let people know when there are substances in the air that should be avoided. Medical researchers have long suspected a link between allergies and cancer, but extensive study on the subject has yielded mixed, often contradictory, results. Many studies have found inverse associations between the two, meaning cancer patients tended to have fewer allergies in their medical history. Other studies have found positive associations, and still others found no association at all, according to a Cornell press release. These findings will appear in the December issue of The Quarterly Review of Biology. In an attempt to explain these contradictions, the Cornell team re-examined nearly 650 previous studies from the past five decades. They found that inverse allergy-cancer associations are far more common with cancers of organ systems that come in direct contact with matter from the external environment - the mouth and throat, colon and rectum, skin, cervix, pancreas and glial brain cells. Likewise, only allergies associated with tissues that are directly exposed to environmental assaults - eczema, hives, hay fever and animal and food allergies - had inverse relationships to cancers. Such inverse associations were found to be far less likely for cancers of more isolated tissues like the breast, meningeal brain cells and prostate, as well as for myeloma, non-Hodgkins lymphoma and myelocytic leukemia. The relationship between asthma and lung cancer, however, is a special case. A majority of the studies that the Cornell team examined found that asthma correlates to higher rates of lung cancer. "Essentially, asthma obstructs clearance of pulmonary mucous, blocking any potentially prophylactic benefit of allergic expulsion," they explain. By contrast, allergies that affect the lungs other than asthma seem to retain the protective effect. So if allergies are part of the body's defence against foreign particle invaders, is it wise to turn them off with antihistamines and other suppressants? The Cornell team said that studies specifically designed to answer this question are needed.
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