Patients with a history of contact allergies may be less likely to develop nonmelanoma skin cancer, brain cancer, and breast cancer, a study has shown.
In research published online July 11 in BMJ Open (doi:10.1136/bmjopen-2011-000084), investigators conversely found diagnoses of bladder cancer more likely in people with a history of contact allergies.
Any protective effects could possibly be explained by the stimulation of natural killer T (NKT) cells through contact allergic reactions, the observational study’s lead author, Kaare Engkilde, Ph.D., of the national allergy research center at Copenhagen University Hospital, said in an interview. "You would probably think that [contact allergy] could lead to skin cancer, but that is not what we found," Dr. Engkilde said.
Contact allergic reactions are delayed reactions caused by chemicals small enough to penetrate the skin – triggers can include perfumes, hair dyes, cobalt, nickel, and formaldehyde. Animal studies have shown that contact allergens have the ability to increase the number of NKT cells, at least temporarily, Dr. Engkilde said.
For their research, Dr. Engkilde and his colleagues used a database of 16,922 Danish patients patch tested for type IV allergies between 1984 and 2008. Of these, 6,065 (35.8%) had at least one positive reaction (26.1% of men, 41.4% of women). Linkage with the Danish Cancer Registry showed 3,200, or 18.9%, of dermatitis patients had a benign tumor, a malignant cancer diagnosis, or both, and 1,207 (37.7%) of these patients had had a positive patch test reaction.
Dr. Engkilde and his colleagues looked specifically at 15 types of cancers, all of which affected at least 40 people in the study population.
The investigators found an inverse association between diagnosed contact allergy and nonmelanoma skin cancer (OR, 0.82) along with breast cancer (OR, 0.80) among both men and women. Dr. Engkilde and his colleagues also noted an inverse trend for brain cancer among women with contact allergies, though the P value was above.05 (OR, 0.36).
The findings related to nonmelanoma skin cancers were on some level expected, Dr. Engkilde said; however, the researchers said they were surprised not to see any protective effect against melanomas.
Dr. Engkilde said his group had no hypothesis for the inverse breast cancer finding, but noted that an earlier study had found that self-reported perfume allergy, a type IV allergy, was related inversely to brain cancer incidence (Am. J. Epidemiol. 2007;166:941-50).
The positive association between contact allergy and bladder cancer (OR, 1.44) was more likely related to accumulations of chemical metabolites of type IV allergens in the bladder than to an effect on NKT cells or another immune response, the investigators said.
They cautioned that the relationships between type IV reactions and cancers were "uncertain and not necessarily the result of causality," and that future analyses would have to adjust for social class and smoking, as the latter can increase the risk of developing nickel contact allergies and several types of cancer.
Also, they wrote, "studies focusing on specific chemical exposures are required to further our understanding of the role of contact allergies in the development of cancer." However, if the relationships are in fact etiologic, the findings have "implications for understanding how contact allergy can affect cancer development and vice versa," they said.
Dr. Engkilde and his coauthors received research support from Aage Bang’s Foundation and the Capital Region’s Research Foundation, and disclosed no competing interests.