Carcinoma cuniculatum of the nail apparatus: report of three cases.

Three patients affected by carcinoma cuniculatum involving the nail apparatus are reported. The toes were affected in 2 cases, the thumb in 1 case. In the first patient the tumour developed in the subungual area and resulted in loss of the toe-nail. In the second patient the tumour originated on the dorsum of the toe and subsequently involved the proximal nail fold. In the third patient the tumour developed in the nail bed resulting in loss of the lateral part of the nail plate. The pathology showed in all cases invaginating strands of well-differentiated keratinocytes, some of which had central crypts containing keratinous debris. Radical excision of the tumour required disarticulation of the digit in 2 cases, whereas Mohs micrographic surgery was performed in the third case.