This fascinating tumor is certainly a rare bird and, like rare birds, it seems to have multiple names: carcinosarcoma, metaplastic carcinoma, carcinoma with sarcomatous component. Take your pick. This lesion comes around once or twice a decade in our practice and was my first case. There is a biphasic proliferation of malignant epithelial and mesenchymal components. The epithelial component shows changes of superficial and solid-type basal cell carcinoma. The basal cell carcinoma component shows intimate association with a spindle cell proliferation that has a somewhat storiform pattern. The spindle cell proliferation also forms a nodule of cells that show nuclear hyperchromasia, pleomorphism and brisk mitotic activity with some atypical mitotic figures. Immunohistochemistry studies showed no staining with epithelial markers in the sarcomatous component.
Basal cell carcinoma with a sarcomatous component (carcinosarcoma): a series of 5 cases and a review of the literature. Rose RF, Merchant W, Stables GI, Lyon CL, Platt A. J Am Acad Dermatol. 2008 Oct;59(4):627-32.