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Case ReportsAbstract
Primary cutaneous carcinosarcoma is a rare malignant biphasic tumor demonstrating both malignant epithelial and mesenchymal components. The epithelial or carcinomatous component presents as a squamous cell carcinoma, basal cell carcinoma, or, rarely, an adnexal malignancy. The mesenchymal or sarcomatous component usually consists of an undifferentiated spindle cell sarcoma or, less frequently, osteosarcoma or chondrosarcoma. The histogenesis of carcinosarcoma is somewhat unknown; however, proposed theories postulate a collision of carcinomatous and sarcomatous components, a common stem cell progenitor cell that diverges and produces both components, and metaplastic transformation of one component to the other. Cutaneous carcinosarcoma commonly presents in elderly males affecting sites of the head and neck associated with repetitive sun exposure. Cutaneous carcinosarcoma has a better prognosis than visceral carcinosarcoma; however, it carries a worse prognosis than conventional cutaneous squamous cell carcinoma. Wide local excision is the mainstay of treatment. Our case describes an 83-year-old male with a 1.4 cm primary carcinosarcoma originating from the nail matrix of the left thumb. Histologically, the lesion contains nests of poorly differentiated squamous cells with central keratinization intimately surrounded by high-grade atypical spindle cells with notable pleomorphism and conspicuous mitotic activity. Immunohistochemistry demonstrates two distinct cell populations with markers of epithelial origin present only in the squamous component. The patient underwent a thumb amputation with no evidence of recurrence or metastatic disease. To our knowledge, few cases of primary cutaneous carcinosarcoma have been reported in the literature with this being the first case of carcinosarcoma arising from the nail bed.