First-line encorafenib + cetuximab + mFOLFOX6 in BRAF V600E-mutant metastatic colorectal cancer (BREAKWATER): Progression-free survival and updated overall survival analyses.

LBA3500 Background: BREAKWATER (NCT04607421) is an open-label, global, randomized, phase 3 study evaluating first-line (1L) encorafenib + cetuximab (EC) ± chemotherapy (chemo) vs standard of care (SOC; chemo ± bevacizumab) in BRAF V600E-mutant metastatic colorectal cancer (mCRC). The study previously met one of its dual primary endpoints (EPs) demonstrating clinically meaningful and statistically significant improvement in confirmed objective response rate (ORR) by blinded independent central review (BICR) in the ORR subset. These results were the basis for the FDA accelerated approval of EC+mFOLFOX6 for BRAF V600E-mutant mCRC, including in the 1L, under Project Frontrunner. Here, we report the primary analysis of progression-free survival (PFS) by BICR, updated interim analysis of OS, updated safety, and other analyses. Methods: Eligible patients (pts) with untreated BRAF V600E-mutant mCRC were randomized 1:1:1 to receive EC, EC+mFOLFOX6, or SOC; EC arm enrollment was closed after a protocol amendment. Dual primary EPs: ORR and PFS by BICR (EC+mFOLFOX6 vs SOC); key secondary EP: OS (EC+mFOLFOX6 vs SOC). Results: 637 pts were randomized to EC, EC+mFOLFOX6, or SOC. Baseline demographics and disease characteristics were generally balanced between arms. EC+mFOLFOX6 (data cutoff: Jan 6, 2025) demonstrated a clinically meaningful and statistically significant PFS improvement vs SOC, meeting the other dual primary EP; HR=0.53 (95% CI 0.407, 0.677; P<0.0001); median PFS 12.8 vs 7.1 mo. OS was clinically meaningful and statistically significant vs SOC; HR=0.49 (95% CI 0.375, 0.632; P<0.0001); median OS 30.3 vs 15.1 mo. Median PFS and OS in the EC arm were 6.8 and 19.5 mo. These data and response data for all randomized pts are shown in the table. Serious treatment-emergent adverse events occurred in 30%, 46%, and 39% of pts in the safety analysis set. Safety was consistent with that known for each agent. Conclusions: BREAKWATER demonstrated clinically meaningful and statistically significant PFS and OS improvements with EC+mFOLFOX6 vs SOC and manageable toxicities. EC+mFOLFOX6 is potentially practice changing as the new SOC. Clinical trial information: NCT04607421 . ECn=158 EC+mFOLFOX6n=236 SOCn=243 EC+mFOLFOX6vs SOCHR (95% CI)P-value a Median PFS b , mo (95% CI) 6.8(5.7, 8.3) 12.8(11.2, 15.9) 7.1(6.8, 8.5) 0.53 (0.407, 0.677) <0.0001 Median OS, mo (95% CI) 19.5(17.6, 22.5) 30.3(21.7, NE) 15.1(13.7, 17.7) 0.49 (0.375, 0.632)<0.0001 ORR, b % (95% CI) 45.6(38.0, 53.3) 65.7(59.4, 71.4) 37.4(31.6, 43.7) Median DOR b , mo (95% CI) c 7.0 (4.2, 11.6) 13.9 (10.9, 18.5) 10.8 (7.6, 13.4) DOR b ≥6 mo, n (%) c 29 (40.3) 110 (71.0) 38 (41.8) DOR b ≥12 mo, n (%) c 15 (20.8) 54 (34.8) 16 (17.6) Median time to response, b wk (range) c 6.6(4.3-86.4) 7.0(5.1-103.6) 7.3 (5.4-48.0) a 1-sided stratified log rank test. b By BICR. c Responders: n=72, n=155, and n=91. DOR, duration of response.