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Cutaneous carcinosarcoma is a biphasic, rare tumor composed of malignant epithelial and mesenchymal components. The most common carcinoma component is a squamous cell carcinoma and the most common sarcoma component is an osteosarcoma. A 74-year-old female patient presented to our hospital with a 3.5×3.5 cm-sized exophytic, eroded tumor surrounded by an erythematous plaque on her right flank that had been present for 10 years. On the incisional biopsy specimen, the tumor was composed of atypical malignant squamous cells and epithelioid cells. Furthermore, immunohistochemistry revealed that the tumor cells were positive to cytokeratin AE1/AE3, cytokeratin 5/6, epithelial membrane antigen, p63, and vimentin but were negative to HMB45, S-100, CD31, CD34, factor VIII, smooth muscle actin, and desmin. Finally, based on these histopathological and immunohistochemical findings, we diagnosed this tumor as cutaneous carcinosarcoma consisting of squamous cell carcinoma and epithelioid sarcoma.
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