Effects of denosumab in patients with bone metastases with and without previous bisphosphonate exposure

Bone metastases place patients at increased risk of skeletal-related events (SREs), including pathologic fractures, spinal cord compression, severe pain requiring radiotherapy or surgery, and hypercalcemia, because of increased osteoclast-mediated bone resorption. Denosumab, a fully human monoclonal antibody, decreases bone resorption by inhibiting RANKL, which mediates osteoclast activity. We compared the effects of denosumab in two phase 2 studies in patients with bone metastases naive to intravenous bisphosphonate therapy (IV BP; n=255) and those with elevated levels of the bone resorption marker urinary N-telopeptide (uNTX) despite ongoing IV BP treatment (n=111). Patients were randomized to receive IV BP every 4 weeks or subcutaneous denosumab every 4 weeks (30/120/180 mg) or every 12 weeks (60/180 mg). Patients treated with denosumab experienced a rapid and sustained reduction in bone turnover regardless of prior IV BP exposure. After 25 weeks, the median uNTX reduction was 75% (IV BP-naive) and 80% (prior IV BP) after denosumab treatment and 71% (IV BP-naive) and 56% (prior IV BP) in the IV BP arms. Denosumab patients with prior IV BP exposure had marked suppression of the osteoclast marker TRAP-5b (median reduction: denosumab 73%, IV BP 11%). SRE incidence was low across both studies. In patients previously treated with BPs, the rate of first on-study SRE was lower in the denosumab groups (8%) than the IV BP group (17%). Denosumab appeared to be well tolerated in both studies. Denosumab suppresses bone resorption markers independently of prior BP treatment, even in patients who appear to respond poorly to BPs.