High-grade trichoblastic carcinosarcoma.

A case of low-grade trichoblastic carcinosarcoma was reported in 2004. Here we present the second case of this tumor, which, in contrast to the original example, may be classified as a high-grade neoplasm. A 92-year-old man presented with an ulcerated lesion on the left ear. The tumor was excised, and the patient had no evidence of recurrence or metastasis 6 years after surgery. Microscopically, the neoplasm demonstrated a fenestrated growth pattern with a slightly myxoid matrix in the background. Two clear components were identified: the first component was clearly epithelial with formation of small round nests, lobules, delicate strands, and small cribriform structures of basaloid cells with some degree of peripheral palisading, nuclear atypia, focal nuclear crowding, and frequent mitotic figures including abnormal forms. Each epithelial aggregation was invariably surrounded by one to three rows of cells with oval to round nuclei, which appeared very similar to specific trichogenic stroma seen in anagen follicles or in trichoblastomas; however, these stromal cells manifested atypical mitoses and cellular pleomorphism. The epithelial and stromal units frequently formed structures identical to follicular papillae associated with germs or "continuous germs" contiguous with "continuous papillae." Despite the close association throughout the tumor, the epithelial and the stromal cells were sharply separated, without transition between both elements. In foci, these stromal cells lost their follicular papillae-like arrangement and proliferated in a diffuse fashion and gradually blended with highly pleomorphic mononuclear spindle-shaped cells and bizarre multinucleated cells that grew in sheets in a highly vascular stroma. Immunohistochemically, the epithelial component showed diffuse staining for cytokeratins (AE1/AE3) and was negative for vimentin and CAM5.2. The stromal cells were positive for vimentin and negative for cytokeratin markers (AE1/AE3) and desmin. We view the present case and that previously reported in 2004 as authentic carcinosarcomas, and not as metaplastic (sarcomatoid) basal cell carcinomas. This conclusion is reached after analyzing the embryological development of the hair follicle, its normal histology and the morphology of cutaneous adnexal tumors with follicular differentiation.