Adnexal carcinomas: A guide to clinical and pathologic diagnosis

Malignant adnexal tumors of the skin are a rare group of neoplasms that are often clinically misdiagnosed. Dermatologists and pathologists frequently struggle to classify these tumors in a logical and orderly manner. The malignant adnexal tumors are categorized into malignant eccrine tumors, apocrine tumors, follicular tumors, and sebaceous carcinoma. We divide malignant eccrine carcinomas into six major types on the basis of histologic criteria, namely tumors with 1) origin from benign eccrine neoplasms, 2) primary ductal differentiation, 3) prominent mucinous stroma, 4) adenoid cystic areas, 5) mucin-secreting and squamoid cells, and 6) a papillary component. Malignant tumors of the hair follicle include malignant proliferating pilar tumors, trichilemmal carcinomas, and pilomatrix carcinomas. Sebaceous and apocrine glands produce sebaceous carcinomas and apocrine carcinomas. The clinical and pathologic findings of these tumors are discussed, with emphasis on features that permit accurate diagnosis and classification.