Real-World Evaluation of Primary Versus Secondary Prevention of Skeletal-Related Events in Metastatic Castration-Resistant Prostate Cancer

Introduction: Anti-osteoclast treatment with denosumab or zoledronate is known to effectively reduce the need for radiotherapy to bone and other skeletal-related events (SREs) in patients with metastatic castration-resistant prostate cancer (mCRPC). In this study, we analyze primary versus secondary initiation of bone-targeting agents (BTAs) relative to first palliative bone radiotherapy in patients dying of mCRPC.

Methods: Provincial administrative databases from Ontario, Canada identified patients with prostate cancer (2007-2018, n = 98 646) who received continuous androgen deprivation therapy (n = 29 453), died of prostate cancer (2013-2018, n = 3864), and received life-prolonging therapy for mCRPC (n = 1850). Variables were collected looking back 3 years from death. Multivariable analysis explored the relationship between clinical variables and BTAs.

Results: Of the 58% (1066/1850) patients with mCRPC who received BTA, only 289 (25.4%) started BTA prior to first palliative bone radiotherapy as primary prevention. Eight hundred and forty-eight (74.6%) patients either never received BTA before death (n = 447) or started BTA only after first bone radiotherapy (n = 401). More patients received denosumab (n = 825, 77%) than zoledronic acid (n = 241, 23%). 51.2% (582/1137) of palliative bone radiotherapy was initiated in the last 12 months of life. Factors associated with the use of BTA included elevated alkaline phosphatase (OR = 1.0, P = .023), de novo metastases (OR = 1.4, P = .005), medical oncologist involvement (OR = 2.0, P = .007), diagnosis 2012-2017 versus 2007-2011 (OR = 0.75, P = .034), and academic center (OR = 0.061, P = .007).

Conclusion: A majority of patients with mCRPC never receive BTAs prior to first SRE, despite universal access and availability of these agents in Ontario. These results highlight an opportunity to improve outcomes by emphasizing early introduction of BTA in patients with mCRPC being started on systemic therapy.