A rare case of atypical pilomatrix neoplasm

Summary: Pilomatrix carcinoma is a rare malignant variant of pilomatricoma that arises from follicular matrix. It commonly presents as a firm nodule ranging from 1-10 cm that often ulcerates. Pilomatrix carcinoma has a predilection for the head and neck region, and it is mostly observed in middle-aged men with the male-female ratio of 4:1. Microscopically, the lesion is characterized by sheets and islands of atypical basaloid cells with infiltrative borders. According to Papadakis et al., presence of 20 mitotic counts per high power field, increased nuclear pleomorphism, and prominent nucleoli are histologically diagnostic. Herein, we report a case of atypical pilomatrix neoplasm of an 80-year-old man presented with a mass on his right cheek measuring 5.3 cm. Microscopically, the lesion showed dermally-based basaloid nests exhibiting asymmetry, irregular borders, and multinodular growth pattern extending to the subcutis. High power showed squamous morules with increased nuclear pleomorphism, prominent nucleoli and scattered mitotic figures. Beta-catenin immunostain was positive for nuclear expression. Follow-up excision showed no evidence of residual disease. Pilomatrix carcinoma has significant recurrence with metastatic potential. Morphologic assessment for architectural and cytologic atypia remains the mainstay of diagnosis.