Nonmelanoma Skin Cancer Risk in Patients With Inflammatory Bowel Disease Undergoing Thiopurine Therapy: A Systematic Review of the Literature

BACKGROUND Azathioprine and 6-mercaptopurine (thiopurines) are common adjunct treatments for inflammatory bowel disease (IBD). Although thiopurine therapy in organ transplant recipients is known to increase nonmelanoma skin cancers (NMSCs), dermatologic literature yields less data regarding NMSC risk of thiopurine use in IBD. OBJECTIVE The aim of this study was to systematically review current literature on NMSC risk in patients with IBD using thiopurine therapy. METHODS Systematic review of PubMed was performed with keywords "inflammatory bowel disease," "ulcerative colitis," "Crohn's disease," "thiopurine," "azathioprine," "6-mercaptopurine," "skin cancer," "non-melanoma," "squamous cell carcinoma," and "basal cell carcinoma." All available publication years were included. Publications were evaluated using PRISMA guidelines. RESULTS The systematic review yielded 67 articles; 18 met final inclusion criteria. LIMITATIONS Heterogeneity of study designs limited direct comparisons of thiopurine exposure and NMSC risk. CONCLUSION Patients with IBD using thiopurines seem to have a moderately increased risk of NMSC that is proportional to therapy duration. Risk of NMSC seems to decrease or return to baseline after discontinuing therapy, although additional data are needed to support this trend. Younger patients with IBD using thiopurines seem to be at greater risk of NMSC. Appreciating NMSC risk in patients with IBD undergoing thiopurine therapy should help direct skin cancer screening recommendations and sun protective measures.