Encorafenib Plus Cetuximab, FOLFIRI Demonstrates Significant PFS Benefit in BRAF V600E-Mutant Metastatic Colorectal Cancer

BRAF V600E mutations occur in approximately 8% to 10% of metastatic colorectal cancer (mCRC) cases and have historically been associated with poor prognosis and limited response to standard chemotherapy.¹

The BREAKWATER phase 3 trial has already reshaped the first-line treatment landscape for this patient population, establishing encorafenib (Braftovi; Pfizer Inc) plus cetuximab (Erbitux; Eli Lilly and Company; EC) combined with mFOLFOX6 as a new standard of care after demonstrating significant improvements in overall response rate (ORR), progression-free survival (PFS), and overall survival (OS) vs chemotherapy with or without bevacizumab.

Now, results from BREAKWATER cohort 3, presented at the 2026 American Society of Clinical Oncology Annual Meeting, extend that evidence base. EC combined with FOLFIRI—an irinotecan-based backbone—delivers clinically meaningful and statistically significant improvements in both ORR and PFS, offering patients and clinicians an important additional first-line option.

Background and Rationale

FOLFOX (folinic acid, fluorouracil, and oxaliplatin) and FOLFIRI (folinic acid, fluorouracil, and irinotecan) are the 2 foundational chemotherapy regimens used in the first-line treatment of mCRC, and while EC plus mFOLFOX6 established the proof of concept for BRAF-targeted combination therapy, not all patients are candidates for an oxaliplatin-based regimen. A prior BREAKWATER safety lead-in had already demonstrated that EC plus FOLFIRI was tolerable with promising antitumor activity, providing the rationale for cohort 3 and the opportunity to validate irinotecan as an alternative chemotherapy backbone in this targeted combination.²

The outcomes observed in BREAKWATER supported the FDA approval of the combination regimen in February 2026 for patients with mCRC with a BRAF V600E mutation.³

“So this supports the use of full theory as an option, in addition to FOLFOX with an EC backbone as a new standard of care for patients with BRAF V600E-mutant mCRC, and this formed the basis for the US FDA approval of EC with a fluorouracil-based chemotherapy for this population,” said Scott Kopetz, MD, PhD, FASCO, an oncologist from the Department of Gastrointestinal Medical Oncology at The University of Texas MD Anderson Cancer Center.⁴

The BREAKWATER Trial

BREAKWATER cohort 3 enrolled 147 patients with untreated BRAF V600E-mutant mCRC, measurable disease by RECIST 1.1, and ECOG performance status of 0 or 1. Patients were randomly assigned 1:1 to receive EC plus FOLFIRI or FOLFIRI with or without bevacizumab as control.²

The primary end point was confirmed ORR by blinded independent central review (BICR); the key secondary end point was PFS by BICR, with OS and safety as additional secondary end points. Median follow-up for PFS was 18.0 months in the EC plus FOLFIRI arm and 14.4 months in the control arm; for OS, follow-up was 20.6 and 20.7 months, respectively, at the January 6, 2026, data cutoff.²

BREAKWATER Met Its Primary End Point

ORR by BICR was 64.4% with EC plus FOLFIRI vs 39.2% with control (OR, 2.76; 95% CI, 1.42-5.35; one-sided P = 0.001), a more than 25 percentage point absolute improvement. The key secondary end point was also met, with EC plus FOLFIRI demonstrating a clinically meaningful and statistically significant improvement in PFS vs control. A prolonged OS benefit was also observed, a particularly noteworthy signal given the historically poor outcomes associated with BRAF V600E-mutant mCRC in the first-line setting.²

The median duration of study treatment was 67.9 weeks in the EC plus FOLFIRI arm vs 32.1 weeks in the control arm—more than double—reflecting the depth and durability of disease control achieved with the targeted combination.²

“Note that 38% of patients on EC and FOLFIRI were still ongoing treatment at the time of the data cutoff, compared to approximately 10% of patients on the control arm,” explained Kopetz. “The duration of treatment was double in the EC FOLFIRI arm of 68 weeks vs 32 weeks in the control arm.”⁴

Consistent Safety Profile

The safety profile of EC plus FOLFIRI was consistent with the known profiles of each individual agent, and no new safety signals were identified. Discontinuation of chemotherapy due to adverse events was similar between arms at 14% for EC plus FOLFIRI vs 10% for control, suggesting that the addition of encorafenib and cetuximab to an irinotecan backbone does not meaningfully increase the rate of treatment-limiting toxicity.²

Clinical Implications for mCRC Treatment

BREAKWATER cohort 3 meaningfully expands the first-line treatment toolkit for patients with BRAF V600E-mutant mCRC. With EC plus mFOLFOX6 already established as a standard of care and EC plus FOLFIRI now demonstrating comparable benefit with an irinotecan-based backbone, clinicians can select the regimen best suited to individual patient characteristics, comorbidities, and toxicity profiles.

“The cohort 3 data support the use of full theory as an option with EC as a new standard of care for this BRAF V600E-mutant [mCRC] population, and highlights the importance of prompt biomarker testing,” concluded Kopetz.⁴

For a patient population that has long faced limited options and poor outcomes, having 2 validated BRAF-targeted first-line combinations represents a significant step toward more personalized, patient-centered care.

REFERENCES

1. Taniguchi H, Uehara K, Ishikawa T, et al. BRAF V600E and non-V600E mutations in RAS wild-type metastatic colorectal cancer: prognostic and therapeutic insights from a nationwide, multicenter, observational study (J-BROS). Cancers (Basel). 2025;17(3):399. doi:10.3390/cancers17030399

2. Kopetz S, Tabernero J, Lonard S, et al. BREAKWATER: progression-free and overall survival analyses of first-line (1L) encorafenib + cetuximab (EC) + FOLFIRI in BRAF V600E-mutant metastatic colorectal cancer (mCRC). Presented at: ASCO 2026; May 28-June 2, 2026; Chicago, IL. Abstract LBA3503.

3. FDA grants traditional approval to encorafenib for metastatic colorectal cancer with a BRAF V600E mutation. FDA. February 24, 2026. Accessed February 24, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-grants-traditional-approval-encorafenib-metastatic-colorectal-cancer-braf-v600e-mutation?utm_medium=email&utm_source=govdelivery

4. Mahmoud N, Wessersmith WA, Folprecht G, et al. Gastrointestinal cancer—colorectal and anal. Presented at: ASCO 2026; May 28-June 2, 2026; Chicago, IL.