[A CASE OF PROSTATE CANCER COMPLICATED BY PELVIC INSUFFICIENCY FRACTURES].

We report a case of high-risk prostate cancer (pT3bN1Gleason score 4＋5), in a 63-year-old male who underwent robot-assisted radical prostatectomy with extended pelvic lymph node dissection in May 2019, followed by adjuvant combined androgen blockade (CAB) therapy. In June 2022, the case progressed to castration-resistant prostate cancer (CRPC), and enzalutamide was initiated. Bone metastases to the sacrum and seventh thoracic vertebra were identified concurrently and treated with radiotherapy. In January 2024, the patient presented with lower back pain and left thigh pain. Computed tomography revealed a right iliac fracture and multiple fractures of the left sacroiliac joint, consistent with radiotherapy-related pelvic insufficiency fractures (PIFs). While PIFs are well-documented in patients with gynecologic malignancies, reports on prostate cancer patients remain limited. We analyzed cases of pelvic fractures following pelvic radiotherapy for prostate cancer at our institution, including the present case, and discussed them in the context of the existing literature.