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Case Reports

Abstract

Basal cell carcinoma (BCC) with sarcomatoid differentiation, or carcinosarcoma, is a rare and aggressive skin tumor containing both epithelial and mesenchymal components, typically occurring on sun-exposed areas of the head and neck. We report a 68-year-old man with a five-year history of a progressively enlarging, tender, erythematous, scaly lesion on the right middle finger, initially diagnosed as a wart. Examination revealed a pink circumferential plaque with a hyperkeratotic nodule obliterating the nail. A tangential biopsy demonstrated pleomorphic spindle cells and dermal hemorrhage. Immunohistochemistry showed CD10 positivity, a vascular stroma highlighted by CD31, and CAM 5.2 and synaptophysin positivity in basophilic areas. SOX10, p63, CK5/6, p40, AE1/AE3, CK20, TTF-1, S100, and chromogranin were negative. CD56 was positive in select spindle cell areas but absent in the basophilic component. MOC-31 and high-molecular-weight keratin were positive in malignant epithelioid clusters. These findings confirmed BCC with sarcomatoid differentiation. The patient underwent radical excision of the right middle finger and sentinel lymph node biopsy, achieving clear margins. This case underscores that carcinosarcoma can present in unusual locations such as digits, mimic benign lesions, and delay diagnosis. Recognition of its biphasic histology with confirmatory immunohistochemistry is crucial. Prompt, complete surgical excision and close surveillance are essential to reduce recurrence and metastasis risk.