P103: Seizure Risk Among Older Adults with Metastatic Castration-Resistant Prostate Cancer Initiating Enzalutamide vs. Abiraterone
Poster Presenter
Ebere Okpara
PhD Candidate
University of Illinois Chicago United States
Objectives
To compare the risk of new seizure events in older men with metastatic castration-resistant prostate cancer (mCRPC) treated with enzalutamide versus abiraterone using real-world data. There is limited evidence of their comparative seizure risk due to a lack of head-to-head clinical trials.
Method
We performed a retrospective cohort study using SEER-Medicare data (2012–2017). Men with prior seizure/antiseizure medication were excluded. The primary outcome was the 1-year risk of seizure. Baseline covariates were balanced using inverse probability weighting and risk estimated with time-to-event
Results
The cohort included 4,910 patients (1,806 enzalutamide initiators, 3,104 abiraterone initiators). The mean age of the study population was 78.0 (SD=6.8) years. Among the cohort, 33% of men had distant (de novo metastatic) disease at diagnosis. During follow-up, 55 seizure events were observed. The one-year cumulative incidence of seizure was 2.1% (95% CI: 1.2%, 2.9%) for enzalutamide and 1.8% (95% CI: 1.1%, 2.5%) for abiraterone, with a corresponding risk ratio (RR) of 1.14 (95% CI: 0.48, 1.81). A post-hoc analysis of outcomes at 6 months was performed, and it showed a stronger difference in the risk of seizure though the confidence interval for the RR was still wide and compatible with the null (RR = 1.88; 95% CI: 0.63, 3.13).
Conclusion
The absolute risk of seizure was low in both abiraterone and enzalutamide treated individuals who did not have a prior seizure history. While there was a slightly higher seizure risk in enzalutamide than abiraterone at 6 and 12 months, precision was limited and the contrast was not statistically nor clinically significant, suggesting concerns about seizure risk may not be critical in treatment selection for MCRPC among those without a prior seizure history.
