Apocrine mixed tumor of the skin with a prominent pilomatricomal component

Abstract

Pilomatrical differentiation within an apocrine mixed tumor (AMT) when present is only focal and has not been reported to be extensive. We herein report an AMT with prominent pilomatrical differentiation. A 47-year-old male presented with a 0.7 cm lesion on the right eyebrow. Histologic sections revealed, underneath a neurofibroma, a well-circumscribed tumor composed of nodules of branching epithelial elements and occasional keratinous cysts within a myxoid and lipomatous stroma. The ductal structures appeared to be composed of two layers of basophilic cuboidal cells and exhibited decapitation secretion. In approximately 50% of the tumor, eosinophilic ghost/shadow cells associated with a foreign body giant cell reaction formed a nodule resembling a pilomatricoma. Focally, columns of matrical cells were seen giving rise to shadow cells. Cytokeratin (CK) 5/6 and CK14 labeled the epithelial component. CK7, CK19 and Ber-EP4 labeled the ductal structures. Carcinoembryonic antigen and epithelial membrane antigen highlighted the luminal surface. S100 stained the stromal cells within the myxoid matrix, adipocytes and spindle cells within the overlying neurofibroma. CK10 highlighted the corneocytes within the keratinous cysts. CK17 labeled the epithelial lining of the keratinous cyst. The presence of follicular and apocrine differentiation within our tumor reinforces the common embryologic derivation of these elements.