Sridhar, Srikala S.

5054 Background: Rucaparib significantly improved radiographic progression-free survival (rPFS) versus physician’s choice of docetaxel or an androgen-receptor pathway inhibitor (ARPI) (abiraterone or enzalutamide) in men with BRCA mutations who were chemotherapy-naïve in the mCRPC setting and had received one prior ARPI in the phase 3 TRITON3 trial (NCT02975934). This post-hoc analysis evaluated whether the timing of prior ARPI therapy impacted the efficacy of rucaparib. Methods: Patients were randomized 2:1 to rucaparib (600 mg BID) or physician’s choice of docetaxel or ARPI, after progression on 1 prior second-generation ARPI in any setting. The primary endpoint was rPFS. Outcomes were analyzed according to whether patients received the prior ARPI in the metastatic castration sensitive (mCSPC) or castration resistant (mCRPC) setting. Data cutoff was August 25, 2022. Results: Of the 302 BRCA1/2 patients, 68 received prior ARPI in the mCSPC setting (42 rucaparib; 26 physician’s choice) and 234 in the mCRPC setting (159 rucaparib; 75 physician’s choice). Baseline characteristics were generally similar. Prior treatments in the mCSPC and mCRPC groups, respectively, included abiraterone (73.5% vs 53.0%), enzalutamide (29.4% vs 48.3%), and docetaxel (17.6% vs 24.8%). Median rPFS favored rucaparib over physician’s choice in both groups (mCSPC: 13.6 vs 8.2 months; HR 0.60 [95% CI, 0.32–1.15]; mCRPC: 11.2 vs 5.8 months; HR 0.43 [95% CI, 0.30–0.61]). Median OS was similar between treatments in both settings (mCSPC: 23.2 vs 21.7 months; HR 0.81 [95% CI, 0.47–1.41]; mCRPC: 23.2 vs 21.0 months; HR 0.91 [95% CI, 0.66–1.25]). Treatment-related adverse events occurred at comparable rates (89.6% vs 86.1%). Conclusions: Rucaparib demonstrated efficacy in patients with BRCA-mutated mCRPC, regardless of whether prior ARPI was administered in the mCSPC or mCRPC setting. Clinical trial information: NCT02975934 .

4514 Background: Maintenance avelumab is a standard of care in patients (pts) with la/mUC who do not progress after first-line PBC. Cabozantinib (CABO) is an oral inhibitor of MET, VEGFR and TAM, active in multiple solid tumors. We hypothesized that an avelumab (Av)-CABO combination would improve outcomes in pts with mUC with an acceptable safety profile compared to avelumab maintenance alone. Methods: MAIN-CAV (NCT05092958) is a phase III randomized, multicenter, international trial for la/mUC pts who did not progress after 4-6 cycles of any PBC (gemcitabine-cisplatin, gemcitabine-carboplatin, MVAC, ddMVAC). Pts were randomized 1:1 to Av 800 mg IV every 2 weeks alone or with CABO 40 mg daily for ≤2 years. Stratification factors were response to first-line PBC (complete response [CR] vs partial response [PR] vs stable disease [SD]) and visceral metastases. The primary endpoint was overall survival (OS); secondary endpoints included progression-free survival (PFS), safety and quality of life. The target accrual was 654 pts; the trial closed early after enrollment of 68 pts following adoption of enfortumab vedotin plus pembrolizumab as the new preferred first-line standard in the US. Results: From 3/2022 to 3/2024, 68 pts were randomized (Av n = 33; CABO-Av n = 35). Median OS was 24.8 months (mo) with Av and 23.0 mo with Avb-CABO (Hazard ratio 1.41; 95% CI 0.66–3.01; p = 0.186). Median PFS was 4.6 mo with Av vs 6.0 mo with Av-CABO (p = 0.343). Objective response rate among pts with PR or SD after first-line PBC was 20.8% with Av vs 11.5% with Av-CABO (p = 0.424). Grade ≥3 treatment-related adverse events occurred in 24.2% pts on the Av arm vs 39.4% of pts on the Av-CABO arm and CABO dose reductions occurred in 63% of pts. Conclusions: Addition of CABO to Av did not improve OS or PFS compared with Av alone in this underpowered, prematurely closed phase III trial; safety was consistent with known profiles. U10CA180821,U10CA180882; U24CA196171, U10CA180863. (CCTG);U10CA180888 (SWOG); https://acknowledgments.alliancefound.org. Clinical trial information: NCT05092958 .