A Recurrent Solitary Fibrous Tumor With an Exceptional Response to Low-Dose Radiotherapy: A Case Report and Literature Review

Solitary fibrous tumor (SFT) is a soft tissue tumor derived from mesenchymal cells. We report a case of a giant SFT with insulin-like growth factor 2 (IGF-2) production in the pelvis of an 85-year-old male. SFT was diagnosed in surgery for a complaint of left lower abdominal distension. Subsequent tumor recurrence and progression caused rectal passage obstruction and hypoglycemia. Low-dose radiotherapy of 15 Gy in five fractions was started five years and four months after surgery, initially for a huge tumor around the rectum to improve rectal passage obstruction. The tumor volume shrank from 1054 cc before irradiation to 449 cc at one month and 396 cc at 10 months after irradiation. He had reached 90 years old at that time. Two months after the initial irradiation, similar radiotherapy of 15 Gy in five fractions was performed for a huge tumor in the right abdominal cavity. This tumor decreased from 1874 cc before irradiation to 615 cc at two months and 556 cc at seven months after irradiation. Dexamethasone (2.5 mg) was used for paraneoplastic syndrome at the time of initial radiation but was then reduced and became unnecessary two months after the second irradiation. Acute and late adverse events were mild. The patient is alive 60 months after the first irradiation. This case suggests that low-dose radiotherapy is beneficial as palliative therapy for symptom relief in patients with SFT.