Thermal keratoses and squamous cell carcinoma in situ associated with erythema ab igne.

A 60-year-old black woman had a large hyperkeratotic lesion and multiple smaller hyperkeratotic papules and plaques on the lower part of her legs in areas of erythema ab igne. Histologic examination of the largest lesion showed hyperplastic carcinoma in situ and the multiple smaller lesions showed varying degrees of squamous cell atypia and dermal elastosis. Histologically, these lesions were identical to solar-induced atypia, indicating that squamous cell carcinoma arising in erythema ab igne may be biologically similar to actinic carcinoma. Discussed here are clinical and histologic features of the thermal-induced lesions and other types of thermal-induced carcinomas.