Risks of Melanoma and Nonmelanoma Skin Cancers Pre- and Post-Inflammatory Bowel Disease Diagnosis.

Background: We compared risks of nonmelanoma skin cancers (NMSCs) and melanoma preceding and following a diagnosis of inflammatory bowel disease (IBD) and to evaluate the effect of thiopurines and anti-tumor necrosis factor α (anti-TNF-α) on skin cancer risk in IBD.

Methods: This was a retrospective, historical cohort study using the population-based University of Manitoba IBD Epidemiology Database (11 228 IBD cases and 104 725 matched controls) linked to the Manitoba Cancer Registry. Logistic and Cox regression analyses were performed to calculate skin cancer risks prior to and after IBD diagnosis.

Results: Persons with ulcerative colitis (UC) were more likely to have basal cell carcinoma (BCC) predating their UC diagnosis (odds ratio, 1.32; 95% confidence interval [CI], 1.08-1.60). Risks of squamous cell carcinoma (SCC), other NMSCs, or melanoma prior to IBD diagnosis were not significantly increased. Post-IBD diagnosis, risks of BCC (hazard ratio, 1.53; 95% CI, 1.37-1.70) and SCC (hazard ratio, 1.61; 95% CI, 1.29-2.01) were significantly increased across all IBD groups except for SCC in UC. There was no significant association between melanoma and IBD post-IBD diagnosis. The risks of BCC and melanoma were increased in thiopurine and anti-TNF users, and risk of SCC was increased in only thiopurine users. Nested cohort analysis of persons with IBD with censoring at both thiopurines and anti-TNF use confirmed a higher baseline risk of BCC and no effect on SCC, comparable to pre-IBD diagnosis findings.

Conclusions: The risk of BCC preceding a diagnosis of UC is higher than in non-UC controls, compared with a generally increased risk of all NMSCs post-IBD diagnosis. Thiopurine and anti-TNF therapy increase the risks for skin cancers in persons with IBD after their diagnoses.