Denosumab and changes in bone turnover markers during androgen deprivation therapy for prostate cancer

Androgen deprivation therapy (ADT) for prostate cancer increases fracture risk, decreases bone mineral density, and increases bone turnover markers (BTMs) including serum type 1 C-telopeptide (sCTX), tartrate-resistant alkaline phosphatase 5b (TRAP-5b), and procollagen-1 N-terminal telopeptide (P1NP). In a prespecified exploratory analysis of a phase 3, multicenter, double-blind study, we evaluated the effects of denosumab (60 mg subcutaneously every 6 months for 3 years) versus placebo (1468 patients, 734 in each group) on BTM values. BTMs were measured at baseline, month 1, and predose at months 6, 12, 24, and 36 in the overall population. BTMs at month 1 are also reported for subgroups based on age (<  70 years versus ≥  70 years), prior duration of ADT (≤  6 months versus > 6 months), and baseline BTM (≤  median versus >  median BTM values). Treatment with denosumab provided a rapid and sustained decrease of BTM values compared with placebo. The median change in sCTX levels at month 1 was -90% in the denosumab group and -3% in the placebo group (p  <  0.0001). The median change in TRAP-5b levels at month 1 was -55% in the denosumab group and -3% in the placebo group (p <  0.0001). The maximal median change in P1NP was -64% in the denosumab group and -11% in the placebo group, (p  <  0.0001). Significantly greater decreases in BTM for denosumab were also seen in subgroup analyses based on age, prior ADT treatment, and baseline BTM values. Suppression of bone turnover markers was consistent with marked increases in bone mineral density reported previously.