Poorly differentiated squamous cell carcinoma arising from an intraepidermal epithelioma.

The intraepidermal epithelioma (of Borst-Jadasson) constitutes a much discussed and debated entity. Currently, this diagnosis is rarely made in part, as ascribing clinical features to such lesions has, to date, proven difficult. In addition, intraepidermal proliferation of atypical cells with clonal features is more likely diagnosed as squamous cell carcinomas in situ, porocarcinomas or inflamed seborrheic keratoses. However, cutaneous tumors exhibiting microscopic and immunohistochemical features of clonally profligate malignant basaloid cells solely of epidermal origin do rarely exist. Their progression to dermal invasion appears even more uncommon.