Molecular correlates of clinical benefit in previously treated patients (pts) with BRAF V600E-mutant metastatic colorectal cancer (mCRC) from the BEACON study.

• DOI: 10.1200/jco.2021.39.15_suppl.3513
• Publication Date: 2021-06-02T14:02:23Z
• Authors: Scott Kopetz; Danielle A. Murphy; Jie Pu; Fortunato Ciardiello; Jayesh Desai; Axel Grothey; Eric Van Cutsem; Harpreet Singh Wasan; Rona Yaeger; Takayuki Yoshino; Amber C Donahue; Adele Golden; Ashwin Gollerkeri; Zhou Zhu; Josep Tabernero
• Keywords: 03 medical and health sciences; 0302 clinical medicine; 3. Good health

3513 Background: Encorafenib + binimetinib + cetuximab (enco/bini/cetux; triplet) and enco + cetux (doublet) regimens improved overall survival and objective response rate vs standard of care in pts with previously treated BRAF V600E-mutant mCRC in the randomized phase 3 BEACON study. To identify molecular correlates of clinical outcome, we performed molecular profiling in tumors from pts in the study. Methods: Baseline tumor samples were retrospectively analyzed by whole-exome sequencing (WES) and whole transcriptome sequencing (WTS) using ImmunoID NeXT (Personalis, Menlo Park, CA, USA). BRAF-mutant (BM) and consensus molecular subtypes (CMS) were determined using published classifiers. Pathway activities were evaluated with gene set variation analysis. Objective tumor response was evaluated according to each subtype. Additional association and interaction analyses between molecular features and clinical outcomes by treatments are ongoing and will be presented. Results: Baseline tumor samples were analyzed by WES and/or WTS from 527 of 665 (79.2%) randomized pts. The biomarker analyses set is representative of the total pt population and had similar clinical outcomes. Of the 460 pts analyzed by WTS (165/224 [73.7%] in the triplet arm, 146/220 [66.4%] in the doublet arm, and 149/221 [67.4%] in the control arm), 84.6% were classified as either CMS1 (n = 225) or CMS4 (n = 164). The proportion of pts classified as BM1 was 32.2% (n = 148) and the majority (84.5%) of these were CMS4, whereas many of those classified as BM2 (67.8%, n = 312) were CMS1 (64.7%). In the BM1 and CMS4 tumors, expression of inflammatory response and epithelial mesenchymal transition genes were elevated, and expression of cell cycle genes was reduced. The response rate in pts with CMS4 and/or BM1 tumors was higher in the triplet arm (CMS4: 33.3% [95% CI: 21.7–46.7]; BM1: 33.3% [95% CI: 21.4–47.1]) compared with the doublet arm (CMS4: 19.2% [95% CI: 9.6–32.5]; BM1: 14.9% [95% CI: 6.2–28.3]). Conclusions: Molecular characteristics and biological properties observed in BRAF V600E-mutant mCRC suggest that a subset of pts with specific molecular features may derive greater clinical benefit from triplet than doublet therapy. Additionally, these findings support the utility of gaining further understanding of the biological landscape in BRAF-mutant mCRC to enable potential hypotheses for pt selection to improve clinical outcome in future studies. Clinical trial information: NCT02928224.