Subtrochanteric fracture in a patient receiving zoledronic acid therapy for metastatic breast cancer.

A 61-year-old woman presented with acute pain of the right thigh after falling on a public street. She had been diagnosed with metastatic breast cancer and bisphosphonate therapy along with zoledronic acid. Radiographs demonstrated transverse subtrochanteric femoral fracture with thickening of the lateral cortex and spike of the medial cortex at the site of fracture. The contralateral femur showed thickening of the lateral cortex at the same site. This type of stress fracture is related to severe suppression of bone turnover (SSBT) under bisphosphonate therapy. Our patient had been receiving zoledronic acid therapy for 3.6 years, and the radiographic findings were typical of stress fracture associated with bisphosphonate. Therefore, the facture in our patient was considered related to SSBT under zoledronic acid therapy. Zoledronic acid is administered to patients with osteoporosis or complications due to cancer such as hypercalcemia of malignancy. Recently stress fractures associated with zoledronic acid therapy for osteoporosis have attracted attention. However, there are few reports of fracture associated with zoledronic acid therapy for cancer. Doses of zoledronic acid recommended for cancer patients are much greater than those for patients with osteoporosis. Clinicians treating such cancer patients need to cautiously manage stress fractures as a complication of zoledronic acid therapy.