Carcinoma cuniculatum (verrucous carcinoma of the skin): a clinicopathologic study of 46 cases with ultrastructural observations.

Forty-six examples of carcinoma cuniculatum, a rare variant of squamous cell carcinoma of the skin, were studied by means of light and electron microscopy and immunoperoxidase techniques. The tumors usually presented as ulcerated, fungating, and polypoid masses with openings of sinus tracts onto the skin surface that exuded foul-smelling greasy material when pressure was applied. On microscopic examination the tumors were seen to be composed mainly of mature squamous keratinocytes with foci of cellular atypia. Electron microscopic studies revealed features of well-differentiated squamous cell carcinoma. The tumor may affect any cutaneous area of the body, and there is a predilection for the feet, particularly the soles. The cause must still be determined, but trauma, chronic irritation, and/or viral infection may play a role. The neoplasm is a low-grade carcinoma capable of local invasion, extension into bone, and rare metastasis to the regional lymph node. Although immunoperoxidase studies revealed no inclusions, infection by human papilloma virus (HPV) remains a possibility.