Invasive Hair Matrix Tumors of the Scalp

Abstract

Fourteen cases of a peculiar, keratinizing invasive epithelial growth occurring on the scalp are reported. These tumors are poorly documented in the literature, but are probably included in some of the reports of carcinomas arising in sebaceous cysts. All of our tumors originally had been diagnosed histologically as carcinoma and often had been considered as carcinoma arising in a sebaceous cyst. Evidence is presented that these tumors show hair follicle differentiation and share some general features with pilomatrixoma or calcifying epithelioma of Malherbe. Invasive pilomatrixoma is proposed as a term for this group of tumors. Although several of our tumors were large and deeply invasive, metastases have not occurred and all have been controlled by local excision or irradiation.