[A Case of atypical Femoral Fracture after Dosing Denosumab]

For the management of patients with castration-resistant prostate cancer with bone metastases, bisphosphonates and denosumab are used to prevent skeletal related events. Osteonecrosis of the jaw and hypocalcemia have been reported in patients treated with denosumab, but there have been few reports of atypical femoral fracture (AFF). Here, we report a case of AFF after dosing denosumab. A 69-year-old man with prostate-specific antigen (PSA) level of 13.08 ng/ml was diagnosed with adenocarcinoma of the prostate, cT3a, N0, M1b, with Gleason score of 4+4=8 and bone metastases to pubis and ischium. Combined-androgen blockade therapy and denosumab were initiated in April 2014. Forty-eight months later, he had left knee pain. He had a magnetic resonance imaging of his left knee, but it showed no obvious findings. However, he had pain in the bilateral thighs and visited the department of orthopedics at our hospital. Pelvic X-ray showed thickening of the bone cortex at the lateral boarders of bilateral femur, and femoral CT showed faint fracture line in bilateral femur. He was diagnosed with AFF, and denosumab was discontinued. Ourcase suggests that we must considerthe possibility of AFF when pain around the thigh occurs after dosing denosumab.