Gingerich, Joel Roger

155 Background: Primary results from the randomized, multicenter, open-label, phase 3 TRITON3 (NCT02975934) study of rucaparib, a poly(ADP-ribose) polymerase inhibitor (PARPi) in patients with chemotherapy-naive mCRPC and BRCA1/2 (BRCA) vs the control arm of physician’s choice of DTX or ARPI (abiraterone acetate [ABI] or enzalutamide [ENZ]) demonstrated that rucaparib significantly improved radiographic progression-free survival (rPFS, primary efficacy endpoint) vs physician’s choice. Here, we report final OS and safety results from TRITON3. Methods: Patients with disease progression after 1 prior second-generation ARPI in any setting were randomized 2:1 to rucaparib 600 mg BID or physician’s choice of DTX, ABI, or ENZ (control). OS was a key secondary endpoint tested initially in the BRCA subgroup, followed by the intent-to-treat (ITT) population in an ordered step-down multiple-comparisons procedure. Crossover from placebo to rucaparib was allowed after radiographic progression was confirmed by independent radiology review. Results: As of March 1, 2024 (final analysis data cutoff),patients with BRCA (N = 302) and ATM (N = 103) alterations were randomized (ITT, N = 405). After an overall median follow-up of 44.0 months, median OS in the BRCA subgroup in the rucaparib arm was 23.2 months vs 21.2 months for the physician’s choice control arm (HR, 0.91 [95% CI, 0.68–1.20]; P = 0.5044; Table). Hierarchical testing did not continue due to lack of statistical significance. No OS benefit was observed in the ITT population or ATM subgroup (Table). Median duration of treatment in rucaparib and physician’s choice arms was 8.3 and 5.1 months, respectively. The most frequent any-grade treatment emergent adverse event (TEAE) in the rucaparib (n = 270) and physician’s choice (n = 130) arms was asthenia/fatigue (61.5% and 63.1%, respectively). The most frequent grade ≥3 TEAE was anemia (23.7%) with rucaparib, and asthenia/fatigue (9.2%) with physician’s choice. Of the 135 patients in the physician’s choice arm, 77 patients had radiographic progression and 70 crossed over to rucaparib. Conclusions: Rucaparib remains the only PARPi to show improved rPFS vs a DTX-containing control arm and has a similar OS even when most patients cross over to rucaparib. Safety was consistent with prior reports. These data support rucaparib as a treatment option for patients with BRCA-mutated mCRPC. Clinical trial information: NCT02975934 . Median OS at final analysis. Group Rucaparib, n Physician's choice, n Rucaparib, months Physician's choice, months HR (95% CI) a BRCA 201 101 23.2 21.2 0.91 (0.68–1.20) ITT 270 135 22.8 21.7 0.99 (0.78–1.26) ATM 69 34 18.4 22.1 1.21 (0.77–1.90) a Calculated by stratified Cox proportional hazard model.

18 Background: TRITON3 (NCT02975934) is a randomized, multicenter, open-label, phase 3 study of rucaparib vs physician’s choice (docetaxel [DTX], abiraterone [ABI] or enzalutamide [ENZ]) in patients (pts) with chemotherapy-naïve mCRPC with BRCA1/2 (BRCA) or ATM alterations. It was previously reported that rucaparib significantly improved the primary endpoint of radiographic progression-free survival (rPFS) vs physician’s choice in pts with BRCA or ATM alterations. We report here the interim overall survival (OS) and also report on efficacy of rucaparib compared individually with either DTX or ABI/ENZ. Methods: Pts had disease progression after 1 prior second-generation androgen pathway inhibitor therapy in any setting and were randomized 2:1 to rucaparib 600 mg BID or physician’s choice of DTX, ABI or ENZ. An ordered step-down multiple comparisons procedure was used to control the overall error rate. OS was a key secondary endpoint with rPFS as the primary endpoint tested first in the BRCA subgroup, then the intent-to-treat (ITT) population. Subgroup analyses based on physician’s choice were exploratory. Results: As of August 25, 2022, 302 pts with BRCA and 103 pts with ATM alterations were randomized. OS maturity was 54% in the BRCA subgroup and 59% in the ITT population. rPFS and OS are shown. The most frequent treatment-emergent adverse event (TEAE) in the rucaparib, DTX and ABI/ENZ groups was asthenia/fatigue (61.1%, 67.6% and 57.6%, respectively). The most frequent grade ≥3 TEAE in the rucaparib, DTX and ABI/ENZ groups was anemia (23.7%), neutropenia (14.1%), and hypertension (10.2%), respectively. Conclusions: Rucaparib significantly improved rPFS vs either DTX or ABI/ENZ; safety was consistent with prior reports. Interim OS results suggest a trend towards improvement for rucaparib vs DTX or ABI/ENZ in pts with mCRPC and BRCA alterations. Clinical trial information: NCT02975934 . [Table: see text]