Background: While the triplet combination of encorafenib (ENCO) + binimetinib (BINI) + cetuximab (CET) indicated higher response rate compared to the doublet combination of ENCO + CET, no significant survival benefits of the triplet combination were observed in patients with BRAF V600E-mutant metastatic colorectal cancer (mCRC) according to BEACON CRC study. Although ENCO + CET is the standard 2^nd-line therapy in the United States and European Union, poor prognoses are expected after disease progression. As resistant mechanisms of BRAF + EGFR blockage, several MAPK pathway alternations, including RAS and RAF mutations were reported, which suggests the additional blockade of MAPK signaling may be an effective strategy for ENCO + CET refractory mCRC. In addition, the preclinical study suggested BRAF inhibitor + anti-EGFR antibody resistant BRAF V600E-mutant colorectal cancer cell-lines were sensitive to the combination of BRAF inhibitor + MEK inhibitor + anti-EGFR antibody (Oddo D, et al. Cancer Res. 2016). Methods: BAYONET is a single-arm multicenter phase II trial to evaluate the efficacy and safety of the staged combination with ENCO + BINI + CET for patients with BRAF V600E-mutant mCRC who were refractory to ENCO + CET. The main eligibility criteria are as follows; RAS wild-type/BRAF V600E-mutant mCRC; age ≥ 20; ECOG PS 0 or 1; within 4 weeks from the last administration of previous ENCO or CET; no administration of other systemic therapy after refractoriness to ENCO + CET; complete response, partial response, or ≥4 months of stable disease were observed in the previous ENCO + CET. Included patients receive the combination treatment of ENCO (300mg once a day) + BINI (45mg twice a day) + CET (400mg/m² initial dose and then 250mg/m² once a week) in a 28 day-cycle as a study treatment. The primary endpoint of this trial is 12-week progression-free survival (PFS) rate. The secondary endpoints include PFS, overall survival, objective response rate, disease control rate, time to treatment failure, and the incidence of adverse events. The targeted sample size was calculated to be 30 on the basis of a power of 80%, a significant level of 10% (one-sided), the threshold 12-week PFS rate of 20%, and the expected 12-week PFS rate of 40%. As a translational analysis, circulating tumor DNA for next-generation sequencing using Guardant360 is collected at twice time points (before and after study treatment) to investigate the resistance mechanisms. Enrollment started from Jan 2022 and is ongoing at 25 facilities in Japan. As of Sep 20, 2022, 9 patients were enrolled. Clinical trial information: jRCTs031210510.