Cutaneous Carcinosarcoma Arising in Basal Cell Carcinoma: A RareDiagnostic Entity

Abstract

Background: Cutaneous carcinosarcoma is an exceptionally rare biphasic malignancy characterised by both epithelial and mesenchymal malignant
components. Because of its aggressive biological behaviour, accurate diagnosis is crucial.

Case Presentation: We report the case of an 87-year-old man with a three-month history of a posterior scalp lesion that began as a keratotic area and evolved to ulceration with intermittent pain. Clinical examination revealed a 3.0 × 1.2 cm ulcerated lesion without regional lymphadenopathy. A clinical impression of squamous cell carcinoma prompted wide local excision. Histopathological assessment identified tumour measuring 8.2 mm in thickness with deep invasion into the reticular dermis and focal extension into subcutaneous fat (pT3). Microscopy demonstrated two intimately admixed components: an infiltrative basal cell carcinoma and a high-grade pleomorphic spindle-cell sarcomatous component. Immunohistochemistry showed dual expression
of epithelial markers together with S100, p63, CD68, and vimentin, supporting the diagnosis of cutaneous carcinosarcoma. The sarcomatous component accounted for the deepest invasion.

Conclusion: This case underscores the need for heightened awareness of cutaneous carcinosarcoma, particularly when encountering sarcomatoid features in lesions arising from common skin cancers. Immunohistochemistry plays an essential role in delineating its biphasic nature and excluding mimics.