The trial met its primary endpoint of time from randomization to first clinical fracture (HR=0.5, 95 percent CI 0.39-0.65, p<0.0001). The observed 50 percent reduction in fractures between the Prolia and placebo arms, 92 versus 176, respectively, was similar in patients with normal bone health at baseline (n=1,872, HR=0.44, p<0.0001) and in patients who started the trial with early signs of bone loss (n=1,548, HR=0.57, p=0.0021).
The data will be presented at the 51st Annual Meeting of the American Society of Clinical Oncology (ASCO) in Chicago today at 9:12 a.m. CT (abstract no. 504). In addition to the presentation, the paper was published online by The Lancet.
This is the first Prolia trial to enroll patients independent of baseline bone mineral density (BMD) and with the majority in the normal BMD range.
The study, which enrolled a total of 3,425 patients, was conducted by the Austrian Breast and Colorectal Cancer Study Group (ABCSG).
"Fracture is a common side effect of aromatase inhibitors, which are an important first-line therapy for postmenopausal women with non-metastatic breast cancer," said principal investigator Michael Gnant, professor of surgery at Medical University of Vienna.
"These encouraging data demonstrate the potential benefit of initiating Prolia simultaneously with aromatase inhibitor therapy, regardless of the patient’s baseline BMD, to decrease the risk of fracture."
Evaluation of key secondary endpoints showed that Prolia reduced the incidence of new vertebral and new or worsening of pre-existing vertebral fractures at 36 months (p<0.01). Statistically significant increases in BMD of the lumbar spine, total hip and femoral neck were observed in the Prolia-treated group at 36 months.
The other secondary endpoints of disease-free survival, bone metastasis-free survival and overall survival have not read out yet.
The safety profile of Prolia therapy was similar to placebo, and no major safety events were reported. The most frequently reported adverse events in this study included arthralgia, hot flush, back pain, osteoarthritis and bone pain.
"Our continued research into Prolia reinforces Amgen’s ongoing commitment to exploring the potential role this medicine can have in breast cancer treatment," said Sean E. Harper, M.D., executive vice president of Research and Development at Amgen.
"Breast cancer patients can be affected by bone loss and its repercussions, and this study provides new evidence of the clinical profile for Prolia in this important setting."
Prolia is the first approved therapy that specifically targets RANK Ligand, an essential regulator of bone-removing cells (osteoclasts).
Prolia is approved in the U.S. for the treatment of postmenopausal women with osteoporosis at high risk for fracture, defined as a history of osteoporotic fracture, or multiple risk factors for fracture; or patients who have failed or are intolerant to other available osteoporosis therapy.