6C-06 - Real-World Radium-223 Utilization Patterns and Survival in Older Men with Metastatic Castration-Resistant Prostate Cancer (mCRPC): A SEER Registry-Linked Medicare Database

Background: Previous research on Ra-223 treatment patterns in metastatic prostate cancer has been limited to select sites, oncology practices, or claims databases. Nationwide studies are needed to better understand Ra-223 treatment patterns and generalize findings across diverse older adult populations.

Objectives: Examine Ra-223 treatment patterns, factors associated with treatment completion, and their associations with real-world overall survival (rwOS) using a nation-wide population database of cancer registries linked to fee-for-service Medicare claims.

Methods: A retrospective cohort analysis was conducted on 1,062 male Medicare beneficiaries (≥66 years) with prostate cancer who initiated Ra-223 treatment between January 2016 and June 2020. Eligible men had 12 months of continuous Medicare Parts A/B/D enrollment prior to Ra-223 initiation and were followed for a minimum of 6 months (follow-up months mean:15.9, median: 12.7 (IQR 8.7-20.1). Primary outcomes included completion of Ra-223 (≥5 cycles without gap ≥ 56 days) and rwOS. Factors influencing Ra-223 completion were analyzed with multivariable logistic regression, and rwOS was estimated using Kaplan-Meier and multivariable proportional hazards regressions.

Results: The cohort was 79.9% non-Hispanic White, 6.8% Hispanic, and 6.1% non-Hispanic Black, with a mean age of 75.6 years (SD=6.6) and median age 75 years (IQR: 70-80) at Ra-223 initiation. Median time to Ra-223 initiation from PC diagnosis was 4 years (IQR: 2-7). Most men were not frail (frailty index < 0.25: 88%). Overall, 59.4% completed approved recommended Ra-223 treatment of ≥5 cycles. Ra-223 layered and combination therapy was utilized in 40% of cohort predominantly with enzalutamide (50.2%) and abiraterone (34.7%). Ra-223 was utilized in 21.1%, 44.1%, and 34.8% of men as first Line (1L), 2L, and ≥ 3L of mCRPC therapy, respectively. Men receiving Ra-223 as 1L therapy (21.1%) (adjusted Odds Ratio (aOR)=1.76, 95% CI [1.22, 2.54], p=0.0026) or 2L therapy (44.1%) (aOR=1.56, 95% CI [1.17, 2.08], p=0.0025) were more likely to complete treatment than those on 3L or later. The median rwOS was 15.0 months [95% CI = 14.3, 15.9]. Completing ≥5 cycles of Ra-223 was associated with longer rwOS(18.5 vs 11.1 months, p< 0.001; aHR=0.51, 95% CI [0.44, 0.59]), as was 1L or 2L therapy use (18.4, 14.8 months vs 13.8 months, p< 0.001;aHR=0.56, 0.82; 95% CI=[0.45, 0.68], [0.69,0.96]) compared to Ra-233 as third-line or later.

Conclusions: Nearly six in ten older men completed the approved recommended Ra-223 treatment cycles. Early initiation of Ra-223 was associated with higher completion rates and better rwOS, underscoring the importance of early Ra-223 use in managing mCRPC.