The US Food and Drug Administration (FDA) has approved denosumab (Prolia, Amgen) to increase bone mass in patients at high risk for fracture receiving androgen- deprivation therapy for nonmetastatic prostate cancer or adjuvant aromatase inhibitor therapy for breast cancer. This monoclonal antibody that binds to RANKL was approved based on results of 2 randomized, double-blind, placebo-controlled trials. One trial randomized 1468 men with prostate cancer. Men aged younger than 70 years were required to have either a baseline bone mineral density (BMD) T score at the lumbar spine, total hip, or femoral neck between -1.0 and -4.0, or history of osteoporotic fracture. The other trial randomized 252 women with breast cancer. Women were required to have a baseline BMD T score at the lumbar spine, total hip, or femoral neck between -1.0 and -2.5 and to have not experienced fracture after age 25. Denosumab use resulted in changes in lumbar spine BMD of +5.6% at 24 months in men and +4.8% at 12 months in women. Those on placebo experienced changes of -1.0% and -0.7%, respectively. Common adverse reactions included arthralgia and back pain. Pain in extremities and musculoskeletal pain were also noted. Hypocalcemia (serum calcium <8.4 mg/dL) was observed only in denosumab-treated patients (2.4%) at the 1-month visit.