Contact allergy may protect against some cancers
MedWire News: Researchers have found that people with allergies to metal and chemicals have a reduced likelihood of developing certain types of cancer, a surprising discovery that could shed light on how the immune system works.
However, the findings are not conclusive and need to be clarified in future studies, say the Danish scientists writing in BMJ Open, an online-only journal.
Previous research has indicated that people who are allergic to substances such as pollen and house dust mites (known as atopy or type 1 allergy) may have a below-average risk for developing cancer.
But it is not known if people with allergies to common metals and chemicals (known as contact or type 4 allergy) might also be protected against the disease.
To investigate, Kaare Engkilde (University Hospital Gentofte, Hellerup) and co-workers studied information on nearly 17,000 Danish adults with dermatitis. This is a nonspecific condition characterized by inflammation of the skin and can have a range of possible causes.
All adults in the study were tested to see if they were allergic to a range of common substances. Over one-third tested positive to at least one allergen and were diagnosed as having contact allergy.
The adults were then monitored for several years, during which time nearly one in five developed tumors of some sort - either cancerous or benign.
The researchers found that people who had tested positive for contact allergy at the start of the study were significantly less likely to develop cancer later in life, including skin, breast, and brain cancer.
The link with brain cancer was true only in women whereas the links with skin and breast cancer were seen in both men and women, the authors remark.
Finally, people with contact allergy at the start of the study were more likely to develop bladder cancer during the follow-up period than were people without contact allergy.
Engkilde and co-authors say their observations support the "immunosurveillance hypothesis," which holds that people with allergies are less likely to develop cancer because their immune systems are super responsive.
In other words, contact allergies may help prime the immune system to ward off certain types of cancer.
Meanwhile, the higher rate of bladder cancer seen in people with allergies may result from higher levels of chemical metabolites accumulated in the blood.
The researchers stress that their findings should be regarded as preliminary and call for the associations to be tested and replicated in future studies.
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By Joanna Lyford