Track: Case Reports

Abstract:

Pilomatrical carcinoma is a locally aggressive malignant neoplasm of follicular matrix cells with a high rate of recurrence, but lower metastatic potential. Pigmented pilomatrical carcinoma (PPC) is an extremely rare variant of pilomatrical carcinoma, also known as malignant melanocytic matricoma, where dendritic melanocytes and melanin are admixed with the tumor cells, imparting a pigmented appearance.^[1]The histology is characterized by asymmetrical, atypical, pleomorphic basaloid cells with prominent nucleoli, shadow cells, and dendritic melanocytes.^[2] Typically, PPC presents in older adult males as firm, pigmented dermal or subcutaneous nodule or ulcerated mass, on the head, neck, and upper trunk region. We report a case of a 95-year-old male who presented with a large, black crusted plaque on the left cheek. A shave biopsy demonstrated polypoid atypical dermal heavily pigmented basosquamous neoplasm with infiltrating pattern and eosinophilic shadow cells, extending to the tissue base. By immunohistochemistry, the tumor cells were positive for beta-catenin (nuclear and cytoplasmic) and pancytokeratin while negative for SOX10, Melan-A, and S-100. These melanocytic markers highlighted the dendritic melanocytic population. Altogether, the findings confirmed the diagnosis of PPC; and Mohs surgery cleared all margins. This report highlights the importance of including PPC in the differential diagnosis of melanoma and pigmented basal cell carcinoma especially on the head and neck lesions in elderly patients. Moreover, it emphasizes the utility of beta-catenin immunohistochemistry in the initial workup to clinch the diagnosis.

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