Background Bone metastases are a major cause of morbidity and mortality in men with prostate cancer. Preclinical studies suggest that osteoclast inhibition may prevent bone metastases. This phase 3 study evaluated denosumab, a fully human anti-RANKL monoclonal antibody, to prevent bone metastasis or death from any cause in men with non-metastatic castration-resistant prostate cancer (CRPC). Methods Men with non-metastatic CRPC at high risk for bone metastasis (PSA ≥8.0 ng/mL and/or PSA doubling time ≤10.0 months) were enrolled in 319 centers from 30 countries. Patients were randomised 1:1 in blinded fashion using an interactive voice response system to receive monthly subcutaneous denosumab 120 mg or placebo. The primary endpoint was bone metastasis-free survival, a composite endpoint determined by time to first occurrence of bone metastasis (symptomatic or asymptomatic) or death. Results 1432 patients were randomised, 716 to receive denosumab and 716 to receive placebo. Denosumab significantly increased bone metastasis-free survival by a median of 4.2 months over placebo (hazard ratio 0.85 [0.73–0.98]; P=0.028). Denosumab also significantly delayed time to first bone metastasis (hazard ratio 0.84 [0.71–0.98]; P=0.032). Overall survival was similar between groups (hazard ratio 1.01 [0.85–1.20]; P=0.91). Rates of adverse events (AEs) and serious AEs were generally similar between groups, except for osteonecrosis of jaw (ONJ) and hypocalcemia. Yearly cumulative incidence of ONJ for denosumab was: 1%, 3%, 4% in years 1, 2, 3, respectively; overall, less than 5% (n=33). Hypocalcemia occurred in under 2% (n=12) of denosumab and under 1% (n=2) of placebo patients. The blinded treatment phase has been completed. Conclusion In men with CRPC, denosumab significantly prolonged bone metastasis-free survival and delayed time to bone metastasis. This is the first large randomised study to demonstrate that targeting the bone microenvironment prevents bone metastasis in men with prostate cancer.

In the current report the lowest testosterone castration level with clinical relevance in medically castrated patients with prostate cancer was 32 ng/dl. Breakthrough increases greater than this threshold predicted a lower survival free of androgen independent progression. Maximal androgen blockade might benefit medically castrated cases of prostate cancer with breakthrough increases of more than 50 ng/dl.

A B S T R A C T PurposeDenosumab, an anti-RANK ligand monoclonal antibody, significantly increases bone metastasisfree survival (BMFS; hazard ratio [HR], 0.85; P ϭ .028) and delays time to first bone metastasis in men with nonmetastatic castration-resistant prostate cancer (CRPC) and baseline prostate-specific antigen (PSA) Ն 8.0 ng/mL and/or PSA doubling time (PSADT) Յ 10.0 months. To identify men at greatest risk for bone metastasis or death, we evaluated relationships between PSA and PSADT with BMFS in the placebo group and the efficacy and safety of denosumab in men with PSADT Յ 10, Յ 6, and Յ 4 months. Patients and MethodsA total of 1,432 men with nonmetastatic CRPC were randomly assigned 1:1 to monthly subcutaneous denosumab 120 mg or placebo. Enrollment began February 2006; primary analysis cutoff was July 2010, when approximately 660 men were anticipated to have developed bone metastases or died. ResultsIn the placebo group, shorter BMFS was observed as PSADT decreased below 8 months. In analyses by shorter baseline PSADT, denosumab consistently increased BMFS by a median of 6.0, 7.2, and 7.5 months among men with PSADT Յ 10 (HR, 0.84; P ϭ .042), Յ 6 (HR, 0.77; P ϭ .006), and Յ 4 months (HR, 0.71; P ϭ .004), respectively. Denosumab also consistently increased time to bone metastasis by PSADT subset. No difference in survival was observed between treatment groups for the overall study population or PSADT subsets. ConclusionPatients with shorter PSADT are at greater risk for bone metastasis or death. Denosumab consistently improves BMFS in men with shorter PSADT and seems to have the greatest treatment effects in men at high risk for progression.