Abstract

Herein we describe a rare case of a biphasic sebaceous carcinoma with sebaceous as well as poorly differentiated sarcomatoid components. A 69-year-old male presented with a 1.5 cm ulcerated nodule on the back that progressed over a 6-month period. The biopsy demonstrated intraepidermal and dermal basaloid areas at the periphery of the lesion, composed of round to polygonal cells with high nuclear to cytoplasmic ratio, irregular nuclei and prominent nucleoli. A few interspersed mature sebocytes with vacuolated, clear cytoplasm and crenulated nuclei were also observed. The vast majority of the lesion showed sarcomatoid areas, composed of spindled and pleomorphic cells reminiscent of an undifferentiated pleomorphic sarcoma. Immunohistological studies showed cytokeratin MNF116 staining in both areas of the tumor, while adipophilin and PRAME mainly highlighted the sebaceous component with only focal expression in the sarcomatoid areas. Microsatellite instability markers (MSH1, MSH2, MSH6 & PMS2) showed retained expression within the tumor cells. Biphasic epithelial and mesenchymal tumors in the skin are referred to by some as “cutaneous carcinosarcomas”. Although most of these cases have squamous cell carcinoma or basal cell carcinoma as the epithelial component, occasional adnexal tumors with sarcomatous foci (such as trichoblastic carcinoma, porocarcinoma and pilomatrical carcinoma) have also been described in the literature. The finding of a sebaceous carcinoma with sarcomatoid differentiation is exceedingly rare and our case highlights the importance of evaluating for sebaceous differentiation in a cutaneous carcinoma with spindle cell/sarcomatoid histomorphology.