Abstract 1395P
Background
Palliative bone radiation is the predominant skeletal-related event (SRE) reported in prostate cancer. Bone targeted agents (BTA), such as denosumab and zoledronic acid, are shown to prevent and delay SREs. This study evaluated real-world use of BTA in relation to palliative bone radiation prior to prostate-cancer related death using linked provincial databases.
Methods
Linked, 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 (≥65 years of age, n=3788). Patients receiving life prolonging therapy (LPT) for metastatic castration-resistant prostate cancer (mCRPC) were selected and use of BTA was identified. Patient characteristics were collected starting 2-years prior to death. Multivariable analyses were conducted to identify factors associated with palliative bone radiation.
Results
1769 patients received LPT for mCRPC, including abiraterone (1094, 62%), docetaxel (881, 60%), enzalutamide (480, 27%), radium-223 (250, 14%) and cabazitaxel (108, 6%). Of these patients, 57% received BTA and 60% received bone radiation. Factors associated with bone radiation were receipt of BTA (95% confidence interval [CI] 1.13-1.91), metastatic disease at diagnosis (CI 1.11-1.97) and radiation oncologist involvement (CI 47.03-226.25), while patients with fewer chronic diseases (CI 0.54-0.98) and who had prior prostatectomy (CI 0.36-0.84) were less likely to undergo bone radiation. The relationship of BTA and bone radiation was maintained for both zoledronic acid (CI 1.09-2.58) and denosumab (CI 1.03-1.77). No specific LPT was associated with use of bone radiation.
Conclusions
Despite clinicians prescribing BTAs to prevent SREs, bone radiation was more likely in patients receiving BTAs. This suggests that clinicians are prescribing BTAs to patients at greater risk of SREs, but patients dying of prostate cancer continue to have significant bone-related morbidity despite contemporary prostate cancer treatment. An analysis of BTA use for primary versus secondary prevention of SREs is being conducted.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Genitourinary medical oncologists of Canada (GUMOC) Astellas Research Grant Program. This work was also supported by ICES (formerly the Institute for Clinical Evaluative Sciences), which is an independent non-profit research institute funded by an annual grant from the Ontario Ministry of Health (MOH) and the Ministry of Long-Term Care (LMTC).
Disclosure
All authors have declared no conflicts of interest.