[Rare and newly described histological variants of cutaneous squamous epithelial carcinoma. Classification by histopathology, cytomorphology and malignant potential].

The histological spectrum of squamous cell carcinoma (SCC) of the skin is presented, including recently mentioned and rarely appearing tumor subtypes. Beside the most frequently occurring common SCC with variable degree of differentiation, the following tumor forms can be identified microscopically: Bowen-SCC, acantholytic SCC, clear cell SCC, spindle cell SCC, keratoacanthoma-like SCC, desmoplastic SCC, neurotrophic SCC, verrucous SCC, adenosquamous carcinoma and basosquamous cell carcinoma. The classification of lymphoepithelioma-like carcinoma as a cutaneous SCC variant is disputed, because epidermal connections are regularly absent and evidence of glandular and follicular differentiation suggest an adnexal origin. Beside the description of distinctive histological and cytomorphological features of each SCC subtype, important differences in malignant behavior and clinical course are emphasized.