Primary mullerian carcinosarcoma of the retroperitoneum: report of a case.

A müllerian carcinosarcoma or malignant mesodermal mixed tumor (MMMT) originated from the retroperitoneum of a 51-year-old woman; only two previous similar cases have been reported. The 1,040 gm tumor was found in the left retroperitoneal space; the center of the tumor was extensively liquified. The uterus, fallopian tubes, and ovaries were unremarkable. The histopathological features of the tumor were typical of MMMT, homologous type. The adenocarcinomatous component of the tumor was immunohistochemically positive for cytokeratin 7 and negative for cytokeratin 20. MMMTs arising in extragenital sites are rare, and most of them arise from the peritoneum. The histogenesis of extragenital MMMTs remains speculative, but the origin from the "secondary mullerian system" is most likely.