(BMJ)—A man in his 60s had an itchy lesion at the site of a smallpox vaccination he received 40 years prior. The lesion developed over 6 months, with no response to topical steroids. Exam: L arm: red macule with thick scales. Bx confirmed the dx. What is it?
Tinea corporis
Melanoma
Eczema vaccinatum
Squamous cell carcinoma
Progressive vaccinia
You are correct. Bx confirmed squamous cell carcinoma. Smallpox immunization with vaccinia virus leaves a slightly depressed, smooth scar at the vaccination site. Although rare, benign and malignant tumors have been reported at these vaccination sites, and have included squamous cell carcinoma, basal cell carcinoma, melanoma, dermatofibrosarcoma protuberans, and malignant fibrous histiocytoma.

BMJ 2022;379:e070440