Abstract
Melanocytic matrical carcinoma (MMC) is a rare tumor of anagen hair follicle origin, thought to be a variant of matrical carcinoma with a component of dendritic melanocytes. Clinically, this presents on sun-damaged skin in older males. Pathology shows a dermal tumor composed of basaloid cells with nuclear atypia and mitoses, admixed with ghost cells and dendritic melanocytes with positive immunostaining for beta-catenin, lymphoid enhancer binding factor 1 (LEF1), and negative staining for BerEp4. The differential diagnosis includes pigmented pilomatricoma, basal cell carcinoma, and malignant melanoma. Histopathologic characteristics including morphology and immunostaining assist with diagnosis of MMC. We report a case of an 84-year-old white male who presented with an erythematous scaly nodule on his right upper back for several months, measuring 1.5 cm x 1.2 cm. Histopathologic examination showed a multilobular tumor with basaloid cells extending through the dermis with overlying epidermal hyperplasia and a collarette of epithelium surrounding the tumor, with no connection to the overlying epidermis. The tumor consisted of lobules of large atypical basaloid cells with central necrosis and scattered mitotic figures and keratin pearls. Melanin pigment was present within the epithelium and surrounding stroma within melanophages. Immunostaining showed high positivity of low molecular weight cytokeratin, p63, and LEF1, and patchy positivity of CK5 and high molecular weight cytokeratin. Immunostaining with MART-1 highlighted the dendritic melanocytes within the periphery of the tumor lobules. Notably, staining for CK20, synaptophysin, TTF-1, and INSM-1 were negative, suggesting this was not a neuroendocrine tumor. Immunostaining for S100, CD117, and BerEp4 was also negative. These characteristics were consistent with MMC. The lesion was treated with excision and closure with no recurrence to date.
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