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Azathioprine Skin Cancer — SCE Dermatology MCQ

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ModerateDermatopharmacologyAzathioprine Skin CancerSCE Dermatology

A 50-year-old man on Azathioprine for pemphigoid develops a new pigmented lesion. His dermatologist notes he has been on long-term Azathioprine for 8 years. What is the specific skin cancer risk with Azathioprine?

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Correct answer: E — Increased risk of SCC (due to UVA-induced DNA photosensitisation from thioguanine metabolites), similar mechanism to other thiopurines

Azathioprine (and its metabolite 6-thioguanine) is incorporated into DNA and photosensitises it to UVA radiation, generating reactive oxygen species and mutagenic DNA damage. This mechanism specifically increases the risk of cutaneous SCC (not BCC or melanoma primarily) in long-term users. The risk is dose- and duration-dependent. Organ transplant recipients on Azathioprine have dramatically elevated SCC risk (65-250× general population). BAD guidelines recommend: rigorous broad-spectrum photoprotection for all patients on long-term thiopurines, regular skin surveillance, and consideration of switching to non-thiopurine immunosuppression (Mycophenolate) in patients developing multiple skin cancers.

Reference: BAD 2011 Azathioprine and Skin Cancer; BJD