Microcystic adnexal carcinoma with extensive sebaceous differentiation.
We report two cases of microcystic adnexal carcinoma showing extensive sebaceous differentiation. Multiple cellular nests and strands within a moderately sclerotic stroma involving the full thickness of the dermis were observed. Clusters of basaloid cells with extensive sebaceous differentiation were present. Foci of sebaceous ductal differentiation were observed in the more superficial areas. Neither strikingly atypical cells nor mitotic figures were present. Perineural invasion was present in the deep areas of both tumors. Clinically, the lesions were solitary whitish-pink papules with a central dell on the faces of 2 men (aged 78 and 73 years old). We propose a relationship between these tumors and other cytologically bland but locally aggressive adnexal carcinomas. Sebaceous differentiation itself in a poorly circumscribed neoplasm does not indicate conventional extraocular sebaceous carcinoma. We propose a simple classification of locally aggressive adnexal carcinomas that takes into account the full range of adnexal differentiation that can occur in such lesions.