Basal Cell Carcinoma with Sarcomatoid Differentiation—A Rare Type and Its Possible Origin

Background: We present an interesting case involving a tumour comprising both basal cell tumour cells and sarcomatoid tumour cells. An 86-year-old woman presented with an erythematous lesion on her left cheek. Clinical and dermoscopic findings suggested BCC. Complete excision and histopathological examination revealed a BCC with a separate proliferation of atypical spindle and epithelioid cells. Immunohistochemical staining supported the diagnosis, with basaloid cells positive for CK5/6 and Ber-EP4 and sarcomatoid cells positive for CD10 and vimentin. Results: Histology and immunohistochemistry confirmed a basal cell carcinoma with sarcomatoid differentiation. The close proximity of sarcomatoid cells to the BCC component suggests a potential role of epithelial–mesenchymal interactions in tumour development. Further investigations into the exact origin of this tumour are required. Conclusion: Basal cell carcinoma with sarcomatoid differentiation is rare. This case highlights the importance of thorough histological and immunohistochemical evaluation. Further studies are necessary to better understand the pathogenesis of such collision tumours.