Real-world use of bone modifying agents in metastatic, castration-resistant prostate cancer

Background Bone modifying agents (BMAs) prevent skeletal related events among patients with metastatic, castration-resistant prostate cancer (mCRPC) involving bone and prevent osteoporotic fractures among patients at high risk. BMA utilization for patients with mCRPC has not been well quantified. Methods We used linked SEER registry and Medicare claims data. We included men diagnosed with stage IV prostate adenocarcinoma during 2007-2015, aged > = 66 at diagnosis, with sufficient continuous enrollment in Medicare Parts A, B, and D, who received androgen deprivation therapy. We limited to those who subsequently received a CRPC-defining treatment (CDT). We identified patients with evidence of bone metastasis using claims. Our primary outcome was receipt of a BMA (zoledronic acid or denosumab) within 180 days of initiating CDT. Results Among 1292 included patients, 1034 (80%) had bone metastasis. BMA use within 180 days of initiating CDT was higher among patients with bone metastases than those without (705/1034 [68%] vs 56/258 [22%]). Among patients without bone metastasis, those with high osteoporotic fracture risk were more likely than those without to receive a BMA (OR = 2.48, 95% CI: 1.17, 5.29); however, only 26% of patients with high fracture risk received a BMA. Among patients who received BMAs, most (62%) first initiated them >90 days before initiating CDT. Conclusions Two-thirds of patients with mCRPC and bone metastases received BMAs within 180 days after initiating CDT. A greater proportion of patients without bone metastasis may warrant BMA therapy for osteoporotic fracture prevention. Some patients with bone metastasis may be able to delay BMA initiation until CRPC.