Hair Matrix Differentiation in a Trichogenic Adnexal Neoplasm.

Abstract

Pilomatricoma is a distinctive tumor characterized by a dual population of proliferating germinative cells and shadow cells and is beleived to derive from the hair matrix. Rarely, benign and malignant adnexal tumors can show pilomaticoma‐like or hair matrix differentiation. We present a 69‐year‐old man with a ruptured cystic nodule of the left cheek. Histology revealed a dermal tumor composed of nests of basaloid cells which manifested peripheral palisading and abortive hair papilla formation with a modified stroma and pilomatricoma‐like areas. This lesion shares features of a trichogenic adnexal neoplasm with those of a tumor having hair matrical differentiation, and has been rarely reported under the designation “follicular” basal cell carcinoma (BCC). This case illustrates an example of this unusual occurrence of hair matrix differentiation in a benign basaloid adnexal neoplasm as characterized by the presence of basaloid and shadow cells; the absence of individual cell necrosis and mitotic activity prompts us to doubt that it represents a form of nodular BCC, but rather it more likely reflects a hamartoma of the follicular anlage.