Atopic Dermatitis and Risk of Skin Cancer A Danish Nationwide Cohort Study (1977-2006)

Background: Recent data suggest a reduced risk of malignant melanoma (MM) among atopic dermatitis (AD) patients, but an increased risk of other skin cancers (including basal cell carcinoma [BCC] and squamous cell carcinoma [SCC]). Objective: We examined the association between AD and skin cancers in a large cohort study in Denmark from 1977 through 2006. Methods: Our cohort consisted of 31 330 AD patients recorded in the Danish National Patient Registry, including AD patients admitted to hospitals and specialized outpatient clinics. Linkage to the Danish Cancer Registry allowed ascertainment of skin cancers. We calculated standardized incidence ratios (SIRs) and associated 95% confidence intervals (CIs) by comparing the incidence rate of skin cancers among AD patients with that among the general Danish population. Results: The overall observed number of MM cases among AD patients was 12, with 21 expected, yielding a SIR of 0.59 (95% CI 0.30, 1.02), with the most pronounced protective effect among AD patients with more than 5 years of follow-up (SIR = 0.46; 95% CI 0.19, 0.95). The corresponding SIRs for BCC and SCC were increased among AD patients (1.41 [95% CI 1.07, 1.83] and 2.48 [95% CI 1.00, 5.11], respectively). Conclusions: Our findings support an inverse association between AD and MM, but an increased risk of BCC and SCC among AD patients.