Primary peritoneal carcinosarcoma arising from the Douglas pouch: A case report.

Primary peritoneal carcinosarcoma is extremely rare and only few cases have been reported in the literature to date. We herein present a case of carcinosarcoma of the Douglas pouch in a 73-year-old Japanese woman. The patient complained of fever and lower abdominal pain, and a large pelvic mass (>10 cm in diameter) was detected, with rectal invasion. Laparotomy was performed and revealed a left ovarian abscess and a Douglas pouch mass; however, there was no obvious tumor involvement of the bilateral ovaries or uterus. The patient underwent total abdominal hysterectomy, bilateral salpingo-oophorectomy and tumor debulking, with a reduction rate of ~30%. Sigmoid colostomy was also performed due to the deep and wide rectal invasion. Histologically, the tumor was composed of a mixture of ovarian high-grade serous carcinoma and spindle-cell sarcoma mimicking leiomyosarcoma. Immunohistochemically, the serous carcinoma component was positive for cytokeratin (CK)7, Wilms' tumor-1 and p53 (null type), while CDX-2 and CK20 were negative. The spindle-cell sarcoma component was positive for vimentin and α-smooth muscle actin. The present case was diagnosed as carcinosarcoma of the homologous type derived from the peritoneum in the Douglas pouch. The patient received several courses of combination chemotherapy with paclitaxel, carboplatin and bevacizumab, and achieved complete remission. The principal treatment for such cases is surgery, and several chemotherapeutic regimens, including paclitaxel and carboplatin, or cisplatin and ifosfamide, have been reported. The accumulation of more clinical cases is crucial for understanding the clinicopathological characteristics of these rare tumors and establishing effective therapeutic strategies.