Cutaneous squamous cell carcinoma arising in chronic discoid lupus erythematosus treated with Mohs micrographic surgery.

Cutaneous squamous cell carcinoma (cSCC) arising within discoid lupus erythematosus (DLE) is a rare but aggressive complication associated with increased rates of recurrence, metastasis, and mortality. Histopathologic overlap between DLE-associated inflammation and cSCC may complicate margin interpretation during Mohs micrographic surgery (MMS). A 63-year-old Hispanic female receiving adalimumab for rheumatoid arthritis, with a longstanding but previously undiagnosed scalp DLE plaque, presented with a progressively enlarging, painful right parietal scalp mass arising at the border of an atrophic alopecic plaque. Histopathologic examination confirmed well-differentiated cSCC arising in a background of DLE. The tumor was successfully treated with MMS and reconstruction using a fish skin substitute. Follow-up demonstrated progressive wound healing without recurrence. This case highlights the malignant potential of chronic DLE lesions and the clinicopathologic challenges encountered during MMS.