Difficulty in distinguishing radiation-induced prostate sarcoma from radiation mucositis in a patient with persistent urinary retention and hematuria after prostate cancer radiotherapy.

Urinary retention and hematuria owing to radiation-induced mucositis are occasional late adverse events in patients with prostate cancer. Moreover, radiation-induced secondary malignancies are late adverse events, although they are extremely rare. Herein, we describe a case of radiation-induced secondary malignancy of the prostate that was initially difficult to distinguish from radiation mucositis. A 74-year-old man with prostate cancer underwent brachytherapy and external beam radiotherapy 9 years ago. Twenty-eight months after irradiation, he presented with urinary retention and hematuria owing to radiation mucositis and underwent transurethral resection of the prostate. At 89 months after irradiation, the patient again showed urinary retention and hematuria. The cause of urinary retention and hematuria could not be identified on cystoscopy. Despite receiving medications, the patient's symptoms did not improve. Therefore, transurethral fulguration was performed, and prostate biopsy revealed spindle cell sarcoma. A diagnosis of radiation-induced undifferentiated pleomorphic/spindle cell sarcoma was made, and the patient underwent total cystectomy and construction of the ileal conduit. Two weeks after the surgery, computed tomography revealed peritoneal dissemination. The patient died 5 weeks after the surgery. The case findings indicate that clinicians should consider the possibility of radiation-induced secondary malignancy; moreover, thorough pathological examination of the prostate with CT and MRI is important to distinguish RISM from radiation mucositis even if no tumors are found on cystoscopy. © The Japan Society of Clinical Oncology 2020.