A hypervascular malignant solitary fibrous tumor in the mesentery of the rectum with good response to preoperative radiation therapy

Solitary fibrous tumor (SFT) is an uncommon neoplasm located in the pelvis. Here, we report a case of hypervascular malignant SFT in the mesentery of the rectum that showed a significant response to preoperative radiotherapy. A 36-year-old man presented to our department with constipation and dysuria. Abdominal computed tomography confirmed a large round neoformation (155 mm in the longest diameter) with an evident contrast-enhanced periphery and a central necrotic area in the pelvis. Considering the results of the examinations, a pelvic neoplasm was strongly suspected. Due to the difficulty of safe gross total removal, a diagnostic laparotomy was indicated. Histologically, hypercellularity with spindle-shaped cells and high mitotic activity was observed. Immunohistochemically, the tumor was positive for CD34, CD99, and bcl-2. The diagnosis of hypervascular malignant SFT was made. After the appropriate information had been given, the patient chose the use of preoperative radiotherapy. After local irradiation, the tumor size regressed to 105 mm in the longest diameter. Laparotomy revealed a tumor originating from the mesentery of the rectum, and the tumor was successfully excised. This case strongly suggested the potential applicability of preoperative radiotherapy for the safe gross total removal of a large pelvic SFT.