Markers of bone metabolism in multiple myeloma patients switched from zoledronic acid to denosumab.

To date, intravenous drip infusion of zoledronic acid (ZA) has mainly been used for the treatment and prevention of skeletal-related events (SRE) in patients with multiple myeloma (MM). Recently, denosumab, a fully humanized monoclonal antibody against receptor activator of nuclear factor-κB ligand (RANKL), has also become available for the same purpose, but little is known about the impact of switching from ZA to denosumab. Herein, we present a retrospective study on bone metabolic markers in 10 MM patients initially treated with ZA and then switched to denosumab. Consequently, the levels of bone resorption markers, tartrate-resistant acid phosphatase 5b (TRACP-5b) and serum type-I collagen crosslinked N-telopeptide (sNTX), significantly decreased after denosumab treatment, while the levels of bone formation markers, osteocalcin (OC) and bone-specific alkaline phosphatase (BAP), showed no apparent changes. No patient developed severe hypocalcemia with denosumab treatment. In one patient not given chemotherapy, the M-protein level increased after switching from ZA to denosumab and plateaued when ZA was restarted. Based on this finding, we anticipate that switching from ZA to denosumab would exert a stronger suppressive effect on osteoclasts, but the anti-myeloma activity of ZA must be taken into consideration.