[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.