Carcinosarcoma of female urethra with melanocytic differentiation.

Carcinosarcoma arising from the female urethra is rare. We report an unusual case of urethral carcinosarcoma from a female patient with melanocytic differentiation. The tumor consists of a high-grade papillary serous carcinoma with psammoma bodies and a mesenchymal component with area of heterologous (cartilaginous) element. More interestingly, there are epithelioid tumor cells containing melanin pigment. On immunohistochemical stains, the epithelioid tumor cells are positive for S100, HMB45 and Mart-1, but negative for cytokeratin. This case represents an unusual carcinosarcoma with areas of melanocytic differentiation. Such rare tumors have been occasionally reported in the breast, uterus, kidney, and lung. These cases demonstrate the capacity of tumor cells to differentiate into divergent elements, supporting the concept of pluripotent tumor stem cells.