Efficacy and Safety of Olaparib Plus Abiraterone Versus Placebo Plus Abiraterone in the First-line Treatment of Patients with Asymptomatic/Mildly Symptomatic and Symptomatic Metastatic Castration-resistant Prostate Cancer: Analyses from the Phase 3 PROpel Trial.

Background and objective: In PROpel (NCT03732820), olaparib + abiraterone resulted in a statistically significant radiographic progression-free survival (rPFS) benefit and numerically prolonged overall survival (OS) versus placebo + abiraterone in first-line (1L) metastatic castration-resistant prostate cancer (mCRPC) patients. Here, we report post hoc exploratory subgroup analyses in patients with asymptomatic/mildly symptomatic or symptomatic disease at baseline.

Methods: Patients were randomised 1:1 to olaparib (300 mg b.i.d.) or placebo with abiraterone (1000 mg o.d.) + prednisone/prednisolone (5 mg b.i.d.). For this post hoc exploratory analysis, patients with a Brief Pain Inventory-Short Form (BPI-SF) item 3 score of <4 and no opiate use were classified as asymptomatic/mildly symptomatic; those with a BPI-SF item 3 score of ≥4 and/or opiate use were classified as symptomatic. Subgroup analyses included investigator-assessed rPFS, OS, objective response rate, time to second progression or death, health-related quality of life, and safety.

Key findings and limitations: The median rPFS in asymptomatic/mildly symptomatic patients (n = 560) was 27.6 mo for olaparib + abiraterone versus 19.1 mo for placebo + abiraterone (hazard ratio [HR], 0.59; 95% confidence interval [CI], 0.46-0.76). For symptomatic patients (n = 183), equivalent values were 14.1 versus 13.8 mo (HR, 0.78; 95% CI, 0.54-1.13). At the final planned OS analysis, the median OS in asymptomatic/mildly symptomatic patients was not reached for olaparib + abiraterone versus 39.5 mo for placebo + abiraterone (HR, 0.77; 95% CI, 0.59-1.00). For symptomatic patients, equivalent values were 22.9 versus 22.8 mo (HR, 0.82; 95% CI, 0.58-1.16). Other outcomes showed no meaningful differences between the subgroups.

Conclusions and clinical implications: Olaparib + abiraterone provided efficacy benefits in 1L mCRPC patients with either asymptomatic/mildly symptomatic or symptomatic disease. A larger benefit occurred in asymptomatic/mildly symptomatic patients.

Patient summary: PROpel, a phase 3 clinical trial, looked at whether combining olaparib with abiraterone delays the progression of patients' cancer compared with placebo plus abiraterone. Patients with or without pain symptoms associated with metastatic castration-resistant prostate cancer were eligible for enrolment into the trial. Results showed that olaparib plus abiraterone reduced the risk of disease progression and death, with a larger benefit observed in patients without or with mild pain symptoms than in those with pain symptoms.