Cancer incidence in 13811 patients skin tested for allergy.

AIM Several studies have shown a negative correlation between cancer and atopy-related diseases. There are also a few reports of a positive relationship. We wanted to further evaluate these relationships in a prospective study. SUBJECTS AND METHODS The incidence of malignant diseases among adult patients with atopy-related diseases (asthma, rhinitis, urticaria, eczema etc; n = 13811), who had been skin prick tested in 1976-1999 was compared with the incidence in the general population. Expected cancer incidence from the date of skin prick testing up to 1999 was obtained from cause-, sex-, calendar-year-, and 5-year-age-group specific incidence rates for the county. These rates were calculated from cancer incidence and population counts obtained from the Swedish Cancer Register. The 95% confidence intervals (CIs) for cause-specific standardized incidence ratios (SIRs) were calculated. Skin prick tests were performed with Dermatophagoides pteronyssinus, horse, dog, cat, timothy, mugwort, birch, and Cladosporium. Patients having one or several positive skin prick test reactions (> or = 2+) were regarded as atopics. RESULTS 119 cases of cancer occurred among 6224 atopic individuals (SIR 1.0) compared with 216 cases (SIR 0.94, CI 0.82-1.08) among 6358 non-atopics. There was a slight excess of Hodgkin's lymphoma cases among atopic men (SIR 4.03, 95% CI 1-10.3), and of non Hodgkin lymphoma cases among atopic women (SIR 4.52, 95% CI 1.23-11.6). However, a large number of comparisons were made which can have caused random findings. CONCLUSIONS The results showed no associations between atopy or allergic symptoms, and subsequent cancer risk, but supported the theory that type-I allergy is not related to cancer risk.