Encorafenib, cetuximab and chemotherapy: a mole against BRAF mutant metastatic colorectal cancer

The identification of key oncogenic drivers and the subsequent development of targeted therapies have significantly improved clinical outcomes of patients with metastatic colorectal cancer (mCRC). These treatment breakthroughs established the role of molecular testing in routine clinical practice and led to the classification of mCRC into four distinct subtypes: microsatellite instability (MSI), RAS mutant, BRAF mutant and RAS/BRAF wild-type.

BRAF is a serine/threonine kinase that conveys signals downstream of RAS by triggering the activation of the mitogen-activated protein kinase (MAPK) pathway. BRAF mutations are categorized into three distinct classes based on their molecular characteristics and biological behavior, with the aim of guiding therapeutic development (1).

Class I mutations, which affect the V600 amino acid, lead to enhanced kinase activity and continuous activation of the MAPK signaling pathway. These mutations function independently of dimerization, with the mutant BRAF proteins signaling persistently as monomers (1,2). The BRAF V600E variant is the most common BRAF mutation in mCRC, accounting for approximately 95% of all BRAF mutations, meaning that the V600E variant is present in the vast majority of these cases with an overall prevalence of 10% (3). BRAF V600E mutant tumors are most frequently observed in female, older patients, right-sided colon cancer, node or peritoneal metastatic involvement, and are enriched in deficient mismatch repair/MSI-high (dMMR/MSI-H). This mutation is associated with unfavorable clinical outcomes and reduced sensitivity to chemotherapy, highlighting the critical role of targeted therapies in the overall treatment approach (3).

Non-V600 BRAF mutations (class II/III) exhibit distinct structural features and signaling mechanisms. Class II mutations function by activating the MAPK signaling pathway through RAS-independent dimerization, while class III mutations have impaired or absent kinase activity and rely on RAS-dependent signaling through heterodimers. Those mutations lack of current targeted options.

The BRAF^V600E mutation has been an important focus of drug development with initially disappointing results in mCRC. Primary resistance to BRAF inhibitors in mCRC is a complex phenomenon driven by multiple mechanisms. Unlike melanoma, where BRAF inhibitor monotherapy shows significant efficacy, mCRC often exhibits intrinsic resistance due to the unique molecular landscape of colorectal tumors, limiting the effectiveness of BRAF inhibitors when used alone. The key mechanisms behind this primary resistance are the activation of alternative pathways, the presence of co-occurring molecular alterations that maintain downstream signaling independent of BRAF inhibition (such as PI3K/AKT/mTOR pathway activation or MET amplification), and a compensatory feedback reactivation of MAPK signaling. Indeed, inhibiting BRAF results in increased expression or activation of receptor tyrosine kinases, particularly EGFR, which restores MAPK pathway activity and diminishes drug efficacy. Further mechanisms of resistance to BRAF inhibitors are the influence of the tumor microenvironment (TME; the surrounding stromal cells and immune components can provide survival signals that help cancer cells evade BRAF-targeted therapy), and the activation of Wnt signaling (ligand-dependent Wnt activation altering drug metabolism and transport mechanisms). To overcome these resistance mechanisms, combination therapies involving BRAF inhibitors, MAPK kinase (MEK) inhibitors, and EGFR inhibitors have been explored to improve treatment efficacy.

The combination of encorafenib, a BRAF kinase inhibitor, and cetuximab, an anti-EGFR monoclonal antibody, is currently available for pretreated mCRC. In 2020, the US Food and Drug Administration (FDA) approved the association of encorafenib with cetuximab (EC) for the treatment of patients with BRAF V600E mutant mCRC. The efficacy and safety of EC was evaluated in the randomized phase III BEACON CRC trial (NCT02928224) (4,5). Eligible patients with BRAF V600E mutant mCRC with disease progression after one or two prior regimens were randomized to receive either EC (experimental arm) or an irinotecan-based chemotherapy with cetuximab (control arm). All efficacy outcomes [overall survival (OS), progression-free survival (PFS) and objective response rate (ORR)] were improved in the EC arm (Figure 1). Median OS was 9.3 months in the EC arm and 5.9 months in the control arm [hazard ratio (HR) for OS, 0.61]. Median PFS was 4.3 months in the EC arm and 1.5 months in the control arm (HR for PFS, 0.44). Confirmed ORR was 19.5% for EC and 1.8% for control (5). The most common adverse reactions (≥25%) for EC regimen were fatigue, nausea, diarrhea, dermatitis acneiform, abdominal pain, decreased appetite, arthralgia, and rash. In 2024, the US FDA granted accelerated approval to EC and FOLFOX as first-line therapy based on efficacy and safety outcomes from the BREAKWATER phase III study (NCT04607421). Patients with previously untreated BRAF V600E mutant mCRC were randomized to receive either EC with chemotherapy, or EC without chemotherapy, or a standard regimen (6,7). PFS, the primary endpoint, and OS were significantly longer with EC-FOLFOX than with standard care (median PFS, 12.8 vs. 7.1 months, HR for PFS, 0.53; P<0.001 and median OS, 30.3 vs. 15.1 months, HR for OS, 0.49; P<0.001). Those survival benefits were observed across all the prespecified clinical subgroups. The study also demonstrated an improvement in ORR, with 66% of patients responding to EC-FOLFOX regimen compared to 37% in the control arm. Beyond efficacy, the safety profile of the combination therapy aligned with the established adverse events of the individual agents. The most common severe adverse reactions (≥5%) for EC-FOLFOX regimen were lipase increased (17%), neutropenia (19%), anemia (15%), neuropathy (8%) and asthenia (5%). This reinforces the feasibility of integrating EC into frontline treatment strategies. Thus, the BREAKWATER study has provided valuable insights into the treatment of BRAF V600E-mutant mCRC, but several key questions remain: what is the optimal chemotherapy regimen (i.e., oxaliplatin-based or irinotecan-based) to combine with encorafenib-cetuximab? Which other anti-tumor drugs could be combined with BRAF inhibitors? How to deal with secondary resistance to BRAF inhibitors? How to treat patients with BRAF V600 mutant dMMR/MSI-H tumors? What is the expected anti-tumor effect in neoadjuvant or adjuvant setting?

Figure 1 Efficacy outcomes of BRAF inhibitors (encorafenib, vemurafenib) in combination with cetuximab in BRAF V600 mutant mCRC studies. No head-to-head comparisons were done across those trials. CI, confidence interval; EGFR, epidermal growth factor receptor; FUP, follow-up; HR, hazard ratio; L, line; mCRC, metastatic colorectal cancer; MSI, microsatellite instability; NA, not applicable; NE, not estimable; NR, not reported; ORR, objective response rate; OS, overall survival; PFS, progression-free survival; SLI, safety-lead-in.

Optimal chemotherapy regimen: oxaliplatin- or irinotecan-based?

Simultaneous use of cetuximab plus vemurafenib, a BRAF inhibitor, combined with irinotecan, was found to be effective in second- or third-line BRAF V600E mutant mCRC, according to results of the randomized SWOG S1406 phase II study (NCT02164916), with an ORR of 17% and a median PFS of 4.2 months (8) (Figure 1). Of note, the PFS treatment effect was similar in patients with MSI-H and microsatellite stable (MSS) status (HR, 0.50). In the safety-lead-in phase of the BREAKWATER study which included 30 patients with BRAF mutant mCRC, the combination of EC plus FOLFIRI demonstrated an acceptable safety profile with no emergent safety concerns, and exhibited encouraging improvements across key efficacy endpoints. First- and second-line ORR were 83% (N=12) and 44% (N=18), respectively (9) (Figure 1). Promising results were also observed in the IMPROVEMENT phase II study, in which 21 patients with BRAF mutant mCRC received vemurafenib-cetuximab with FOLFIRI as first- or second-line setting, with an ORR of 81% and a median PFS of 9.7 months (10) (Figure 1). In the ongoing cohort 3 of BREAKWATER study, patients are being randomized between FOLFIRI-EC and FOLFIRI-bevacizumab. The primary endpoint is ORR.

Which other anti-tumor drugs could be combined with BRAF inhibitors?

MEK and ERK inhibitors

Targeting the MAPK pathway is essential in the therapeutic management of BRAF-mutant mCRC. Indeed, BRAF inhibitors alone often lead to adaptive resistance, primarily through reactivation of the MAPK pathway via MEK and ERK signaling. This limits their effectiveness, as tumors can bypass BRAF inhibition and continue proliferating. MEK and ERK inhibitors directly target the downstream effector of this pathway, preventing reactivation and sustaining tumor suppression. Hence, therapeutic approaches targeting this pathway require refinement to effectively address both intrinsic and treatment-emergent resistance mechanisms. Studies have shown that dual inhibition of BRAF and MEK leads to greater tumor growth reduction, apoptosis, and immune activation. The combination of EC and binimetinib (ECB) resulted in significantly longer OS and a higher ORR than standard therapy in patients with previously treated BRAF V600E mutant mCRC (BEACON CRC, NCT02928224) (4). The ANCHOR CRC (NCT03693170) phase II study suggested that the ECB regimen was also active in the first-line setting of BRAF^V600E-mutated mCRC with a manageable safety profile (11). Several other MEK inhibitors such as trametinib and cobimetinib have also been evaluated in combination with BRAF inhibitors to enhance MAPK pathway suppression in BRAF mutant colorectal cancer (CRC) (12-14). Further selective MEK1/2 inhibitors, such as tunlametinib (NCT06008119) or PAS-004 (NCT06299839) and ERK inhibitors, such as ERAS-007 (NCT05039177), LY3214996 (NCT04534283), LTT462 (NCT04294160) and ulixertinib (NCT04488003) are being evaluated in BRAF mutant mCRC ongoing trials.

Antiangiogenic agents

Preclinical evidence indicates that increased expression and activation of vascular endothelial growth factor A (VEGF-A) may play a role in mediating resistance to BRAF inhibitor therapy in CRC. The ongoing BRAVE (NCT06411600) phase II study evaluates the efficacy of the combination therapy of EC and bevacizumab, an anti-angiogenic agent targeting VEGFA, in patients with previously treated BRAF mutant mCRC.

Immunotherapy

BRAF inhibitors have the potential to modify the TME by increasing immune infiltration and antigen presentation, thereby enhancing the effectiveness of immunotherapy even in MSS tumors. Several ongoing trials are evaluating BRAF inhibitors in combination with immunotherapy for MSS BRAF-mutant CRC (nivolumab, NCT04017650; spartalizumab or tislelizumab, NCT04294160).

Agents targeting TME

TME contributes to adaptative resistance to BRAF inhibitors via stromal and immune cells. Components of the TME, such as fibroblasts, myeloid-derived suppressor cells, and regulatory T cells, can secrete cytokines and growth factors that reactivate MAPK or PI3K pathways, bypassing BRAF inhibition. Thus, combining BRAF inhibitors with agents targeting the TME (e.g., anti-VEGF, anti-CSF1R) could overcome resistance.

How to deal with secondary resistance to BRAF inhibitors?

Several approaches are particularly relevant for overcoming resistance mechanisms that arise with selective BRAF inhibitors: treatment beyond progression, treatment rechallenge or enlarging BRAF inhibition. Maintaining a BRAF inhibition beyond progression is being evaluated in patients with BRAF mutant mCRC with disease progression while being treated with EC, by continuing the doublet and adding either chemotherapy (ECLYPse, EudraCT 2023-508615-24-00) or MEK inhibitor (BAYONET, jRCTs031210510). Rechallenging EC is being evaluating in several phase II studies, either alone (BRICKET, EudraCT 2023-509088-26-00) or in combination with binimetinib MEK inhibitor (TRIDENTE, jRCTs031210511) Pan-RAF inhibition is a therapeutic strategy designed to target all RAF isoforms simultaneously (XP-102, NCT05275374; BDTX-4933, NCT05786924).

How to treat patients with BRAF V600 mutant dMMR/MSI-H tumors?

Standard first-line therapy in dMMR/MSI-H mCRC is immunotherapy, being a highly effective treatment in this subgroup. While immune checkpoint inhibitors like doublet nivolumab-ipilimumab or pembrolizumab single agent have shown impressive efficacy in MSI-H mCRC, not all patients with MSI tumors respond to immunotherapy. Up to 15–30% of patients may exhibit primary resistance that may be linked to differences in the TME, such as stromal composition and immune cell infiltration. Adding chemotherapy or targeted agents to immunotherapy may improve treatment efficacy. SEAMARK (NCT05217446) is a randomized phase II study evaluating the therapeutic effect of pembrolizumab with encorafenib and cetuximab compared to pembrolizumab alone in treatment-naive patients with BRAF V600E-mutant dMMR/MSI-H mCRC.

What is the expected anti-tumor effect in neoadjuvant or adjuvant setting?

In the neoadjuvant setting, BRAF inhibitors may help shrink tumors before surgery, potentially increasing the likelihood of complete resection. But, there is a growing concern about inappropriate and/or overtreatment in early-stage tumors when applying targeted therapies that are primarily validated in the metastatic setting, leading to unnecessary toxicity. While BRAF V600E mutations are associated with poor prognosis in metastatic CRC, their prognostic role in early-stage tumors is more nuanced. This underscores the need for better predictive biomarkers to distinguish which early-stage patients could benefit from the addition of BRAF inhibitors in the neoadjuvant setting. The FOxTROT4 (EUdraCT 2021-002216-31) and the AIO-KRK-0420 NeoBRAF (NCT05510895) evaluate EC or ECB, respectively, as neoadjuvant therapy in patients with unresected BRAF mutant localized colon cancer. The NEXUS trial (jRCT2031220025) is evaluating the ECB triplet regimen in surgically resectable BRAF-mutant colorectal oligometastases, aiming to improve PFS.

The BREAKWATER study represents a significant milestone in CRC research, bringing renewed optimism to patients with BRAF V600E mutant tumors. By combining EC and FOLFOX chemotherapy, the trial aimed to preempt or delay resistance mechanisms that typically emerge with BRAF-targeted therapy alone. This combination targets multiple steps in the MAPK pathway and beyond, reducing the likelihood that tumor cells can bypass the blockade through compensatory signaling. Based on those positive results, the addition of chemotherapy to a dual therapy targeting BRAF and EGFR becomes the standard first-line therapy in patients with previously untreated MSS BRAF V600 mutant mCRC. This trial also paves the way for groundbreaking advancements in precision oncology, shaping the future of targeted therapies.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, AME Clinical Trials Review. The article has undergone external peer review.

Peer Review File: Available at https://actr.amegroups.com/article/view/10.21037/actr-25-80/prf

Funding: None.

Conflicts of Interest: The author has completed the ICMJE uniform disclosure form (available at https://actr.amegroups.com/article/view/10.21037/actr-25-80/coif). B.C. reports receiving payment from Pierre Fabre. The author has no other conflicts of interest to declare.

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References

1. Dankner M, Rose AAN, Rajkumar S, et al. Classifying BRAF alterations in cancer: new rational therapeutic strategies for actionable mutations. Oncogene 2018;37:3183-99. [Crossref] [PubMed]
2. Poulikakos PI, Persaud Y, Janakiraman M, et al. RAF inhibitor resistance is mediated by dimerization of aberrantly spliced BRAF(V600E). Nature 2011;480:387-90. [Crossref] [PubMed]
3. Cohen R, Liu H, Fiskum J, et al. BRAF V600E Mutation in First-Line Metastatic Colorectal Cancer: An Analysis of Individual Patient Data From the ARCAD Database. J Natl Cancer Inst 2021;113:1386-95. [Crossref] [PubMed]
4. Kopetz S, Grothey A, Yaeger R, et al. Encorafenib, Binimetinib, and Cetuximab in BRAF V600E-Mutated Colorectal Cancer. N Engl J Med 2019;381:1632-43. [Crossref] [PubMed]
5. Tabernero J, Grothey A, Van Cutsem E, et al. Encorafenib Plus Cetuximab as a New Standard of Care for Previously Treated BRAF V600E-Mutant Metastatic Colorectal Cancer: Updated Survival Results and Subgroup Analyses from the BEACON Study. J Clin Oncol 2021;39:273-84. [Crossref] [PubMed]
6. Kopetz S, Yoshino T, Van Cutsem E, et al. Encorafenib, cetuximab and chemotherapy in BRAF-mutant colorectal cancer: a randomized phase 3 trial. Nat Med 2025;31:901-8. [Crossref] [PubMed]
7. Elez E, Yoshino T, Shen L, et al. Encorafenib, Cetuximab, and mFOLFOX6 in BRAF-Mutated Colorectal Cancer. N Engl J Med 2025;392:2425-37. [Crossref] [PubMed]
8. Kopetz S, Guthrie KA, Morris VK, et al. Randomized Trial of Irinotecan and Cetuximab With or Without Vemurafenib in BRAF-Mutant Metastatic Colorectal Cancer (SWOG S1406). J Clin Oncol 2021;39:285-94. [Crossref] [PubMed]
9. Tabernero J, Yoshino T, Kim TW, et al. Encorafenib + cetuximab (EC) + FOLFIRI for BRAF V600E-mutant metastatic colorectal cancer (mCRC): Updated results from the BREAKWATER safety lead-in (SLI). Presented at: 2024 ESMO Congress; Barcelona, Spain. Abstract 515MO; September 13-17, 2024.
10. Wang Z, Qin BD, Ye CY, et al. Cetuximab and vemurafenib plus FOLFIRI (5-fluorouracil/leucovorin/irinotecan) for BRAF V600E-mutated advanced colorectal cancer (IMPROVEMENT): An open-label, single-arm, phase II trial. Eur J Cancer 2022;163:152-62. [Crossref] [PubMed]
11. Van Cutsem E, Taieb J, Yaeger R, et al. ANCHOR CRC: Results From a Single-Arm, Phase II Study of Encorafenib Plus Binimetinib and Cetuximab in Previously Untreated BRAF(V600E)-Mutant Metastatic Colorectal Cancer. J Clin Oncol 2023;41:2628-37. [Crossref] [PubMed]
12. Corcoran RB, Atreya CE, Falchook GS, et al. Combined BRAF and MEK Inhibition With Dabrafenib and Trametinib in BRAF V600-Mutant Colorectal Cancer. J Clin Oncol 2015;33:4023-31. [Crossref] [PubMed]
13. Corcoran RB, André T, Atreya CE, et al. Combined BRAF, EGFR, and MEK Inhibition in Patients with BRAF(V600E)-Mutant Colorectal Cancer. Cancer Discov 2018;8:428-43. [Crossref] [PubMed]
14. Klute KA, Rothe M, Garrett-Mayer E, et al. Cobimetinib Plus Vemurafenib in Patients With Colorectal Cancer With BRAF Mutations: Results From the Targeted Agent and Profiling Utilization Registry (TAPUR) Study. JCO Precis Oncol 2022;6:e2200191. [Crossref] [PubMed]