Late last week, on Sept. 16, the FDA approved denosumab to increase bone mass in patients receiving treatment for hormone-positive breast or prostate cancer who are at risk of bone fracture due to treatment.Denosumab works by binding to RANKL, a protein involved in the formation, function and survival of osteoclasts, cells that break down bone tissue. In patients with hormone-positive cancers, treatments, such as aromatase inhibitors or androgen-deprivation therapy, can further weaken bones. The new approval of denosumab, under the brand name Prolia, is the first therapy to treat bone loss in patients with these types of cancers. In mid-2010, Prolia received FDA approval to reduce the risk of fractures in women with osteoporosis. Xgeva, another form of denosumab, was approved in late 2010 to reduce fractures in certain advanced cancer patients with bone metastases. The new indication was approved as Prolia because it is the same dosage used for women with osteoporosis - 60 mg subcutaneous injection that is give once every six months. Xgeva is given as a 120 mg injection every four weeks. In the two trials reviewed by the FDA for this recent approval, Prolia increased bone mineral density when compared with placebo at one and two years follow-up. In prostate cancer patients, Prolia decreased new vertebral fractures at three years. Reported side effects included joint and back pain. You can read about the approval and studies the FDA based its decision on here.You can also view an animation of how certain cancer treatments affect bone tissue here.