Impact of Monthly 120 Mg Denosumab on Bone Metabolism in Bone-metastatic Prostate Cancer Undergoing Androgen Deprivation Therapy

Abstract

Background: While semiannual 60 mg denosumab is a common treatment for osteoporosis, impact of monthly 120 mg denosumab, the common treatment protocol for bone metastases from solid tumors, on bone metabolism is unclear.Materials and Methods: We reviewed 15 patients with bone-metastatic prostate cancer who initiated monthly 120 mg denosumab in conjunction with androgen deprivation therapy between 2013 and 2014. Bone mineral density (BMD) was measured at lumbar spine and femoral neck using dual energy X-ray absorptiometry (DXA), before treatment and annually thereafter. Bone metabolism markers, including urine N-terminal telopeptide (uNTx) and bone type alkaline phosphatase (BAP), were monitored monthly.Results: Twelve of 15 (80%) patients had evaluable DXA before treatment, and of them, eight underwent DXA after a year of initiation without discontinuation of denosumab. Percent changes in BMD from baseline were +6.2% at lumbar spine and +7.6% at femoral neck, both of which were significant increases (both P<0.01). Bone metabolism markers were evaluable in 11 (73%) patients: uNTx decreased rapidly, while BAP declined gradually after initiating denosumab. These effects were similar to those seen by the standardized dose for osteoporosis in previous literature. There were no denosumab-related severe adverse events during the follow-up period. Conclusions: The impact of monthly 120 mg denosumab on bone metabolism was significant, but almost equivalent to that of the standard dose for osteoporosis (60mg semiannually) in bone-metastatic prostate cancer undergoing androgen deprivation therapy. Whereas the higher dose has reportedly reduced skeleton-related events, the effect on bone metabolism seemed plateaued or showed no dose-dependency.