Real-world associations between bone-targeted agents and palliative bone radiotherapy in prostate cancer decedents: A province-wide population study.

Abstract

e17043 Background: Palliative bone radiation is the predominant skeletal-related event (SRE) reported in advanced prostate cancer. Bone targeted agents (BTA), such as denosumab and zoledronic acid, are shown to both prevent and delay SREs including bone radiation. This study evaluated real-world use of BTA in a large provincial database in relation to palliative bone radiotherapy prior to prostate-cancer related death. Methods: Linked, province-wide administrative databases from Ontario, Canada identified patients with prostate cancer (2007-2018, n = 98646), who received continuous androgen deprivation therapy (n = 29453), died between 2013-2018 (n = 4184), and qualified for Ontario Drug Benefits (OBD; 65 years or older, n = 3788). Patients receiving novel life prolonging therapy (LPT) for metastatic castration-resistant prostate cancer (mCRPC; abiraterone, enzalutamide, docetaxel, cabazitaxel and radium-223) were selected, and use of BTA (denosumab, zoledronic acid) was identified. Demographic, health, and treatment characteristics were collected over a 2-year observation window looking back from the date of death. Multivariable analyses were conducted to identify factors important in use of palliative bone radiation. Results: 1769 patients received LPT for mCRPC, including abiraterone (n = 1094, 62%), docetaxel (n = 881, 60%), enzalutamide (n = 480, 27%), radium-223 (n = 250, 14%) and cabazitaxel (n = 108, 6%). Amongst patients receiving LPT, 57% received BTA and 60% received palliative radiation to bone. Factors associated with palliative bone radiation were receipt of BTA (OR 1.46; 95% confidence interval [CI] 1.13-1.91), metastatic disease at diagnosis (OR 1.48; CI: 1.11-1.97), radiation oncologist involvement (OR 103.11; CI: 47.03-226.25), whereas patients with fewer chronic diseases (OR 0.73; CI: 0.54-0.98) and who had prior prostatectomy (OR 0.54; CI: 0.36-0.84) were less likely to receive radiation. This relationship was maintained for both zoledronic acid (OR 1.68; CI: 1.09-2.58) and denosumab (OR 1.35, CI: 1.03-1.77). No specific LPT was associated with use of palliative bone radiation. Conclusions: Despite clinicians prescribing BTAs to prevent SREs, in this cohort, radiotherapy to bone was more likely in patients receiving BTAs. This suggests that clinicians are prescribing BTAs to patients at greater risk of SREs, but that patients dying of prostate cancer continue to have significant bone-related morbidity despite contemporary prostate cancer treatment. An analysis of primary (before bone radiotherapy) versus secondary (after bone radiotherapy) BTA prescriptions will be presented, as well as timing of BTA initiation in relation to death.