Patients with a history of contact allergy may be less likely to develop non-melanoma skin cancer, brain cancer or breast cancer, but more likely to develop bladder cancer, a study in Denmark has found. Dr Kaare Engkilde of the National Allergy Research Centre at Copenhagen University Hospital, and colleagues used a database of nearly 17,000 Danish patients patch tested for type 4 allergies between 1984 and 2008.

Contact allergies are a type 4 allergy where the person has a reaction when they come into contact with common metals and chemicals. Triggers can include perfumes, nickel, hair dyes and formaldehyde. Previous research has indicated that people with type 1 allergies, which include pollen and dustmites, may be more or less likely to develop cancer.

Animal tests have shown that contact allergens have the ability to increase the number of natural killer T (NKT) cells, at least temporarily, so they theorised that any protective effects against cancer could be explained by the stimulation of NKT cells through the contact allergic reactions. The findings of this study back up the “immunosurveillance hypothesis”, which holds that people with allergies are lees likely to develop cancer because their immune systems are super responsive.

Of the 17,000 participants, 35.8% had at least one positive reaction to a skin patch test. By comparing the findings to the Danish Cancer Registry, they found that 18.9% of dermatitis patients had a benign tumour, a malignant cancer diagnosis or both, and 37.7% of these patients had had a positive patch test reaction.

Looking at specifically the 15 types of cancer which affected at least 40 people in the study population, Dr Engkilde and colleagues found an inverse association between diagnosed contact allergy and nonmelanoma skin cancer and breast cancer among men and women. There was also an inverse trend for brain cancer among women.

They had no idea why there would be an inverse trend for breast cancer, but that a previous study had found that self-reported perfume allergy was related inversely to brain cancer incidence.

The positive association between contact allergy and bladder cancer was more likely to relate to accumulations of chemical metabolites of type iv allergens than to an effect on NKT cells.

Future analyses would have to adjust for social class and smoking habits, as smoking can increase the risk of developing nickel contact allergies and several types of cancer, but the findings do have implications for understanding how contact allergy can affect cancer development.

Source: British Medical Journal  

First published in July 2011

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