Basal cell carcinoma with hyaline inclusions.

A 69 yr old man had a 4 mm basal cell carcinoma completely excised from the chin. Numerous hyaline cytoplasmic inclusions were contained within the tumor cells. The inclusions stained intensely red with Masson's trichrome, and immunocytochemically there was prominent rim labelling for keratins (bovine, callus and AE1/3) and muscle-specific actin, the latter more faintly decorating the centre of some inclusions. The inclusions were negative for antibodies to cytokeratin Cam5.2, epithelial membrane antigen (EMA), vimentin, S100, neurofilaments, glial fibrillary acidic protein (GFAP) and carcinoembryonic antigen (CEA) and there was no post Congo red apple green birefringence to indicate amyloid. Ultrastructure indicated the inclusions were composed of proteinaceous material surrounded by a defined rim of tonofilaments in cells showing no degenerative features. The findings suggested aberrant tumor cell keratinization. Familiarization with this rare variant of a common cutaneous carcinoma will alleviate diagnostic difficulties that may arise, particularly in superficial tumor curettage.