First-line encorafenib plus binimetinib and pembrolizumab for advanced BRAF V600-mutant melanoma: Safety lead-in results from the randomized phase III STARBOARD study.

Background: BRAF inhibitors plus MEK inhibitors (BRAFi/MEKi) and immune checkpoint inhibitors (CPIs) are approved for BRAF V600-mutant advanced melanoma. Combinations of BRAFi/MEKi with CPIs may further improve outcomes and could offer additional treatment strategies.

Methods: STARBOARD (NCT04657991) is a phase III study with an initial safety lead-in (SLI) phase conducted to determine the recommended phase III dose (RP3D) for encorafenib in combination with binimetinib and pembrolizumab. Patients with untreated, unresectable locally advanced or metastatic BRAF V600E/K-mutant cutaneous melanoma received binimetinib 45 mg twice daily and pembrolizumab 200 mg every 3 weeks plus encorafenib 450 mg once daily (COMBO450 plus pembrolizumab) or 300 mg once daily (COMBO300 plus pembrolizumab). The primary endpoint was the incidence of dose-limiting toxicities (DLTs). Secondary endpoints included safety, objective response, time to response, and duration of response. Progression-free survival was assessed post hoc.

Results: In the SLI, the median follow-up duration was 19.4 months. Twenty patients received COMBO450 plus pembrolizumab and 17 received COMBO300 plus pembrolizumab. DLTs occurred in 1 of 17 DLT-evaluable patients in the COMBO450 plus pembrolizumab arm and in 2 of 17 DLT-evaluable patients in the COMBO300 plus pembrolizumab arm. No treatment-related deaths occurred in either treatment arm. The overall response rate was 65.0 % in the COMBO450 plus pembrolizumab arm and 47.1 % in the COMBO300 plus pembrolizumab arm.

Conclusion: The STARBOARD SLI showed that safety across the cohorts was generally comparable to the known safety profile of each agent. The standard dose regimen of COMBO450 plus pembrolizumab was chosen as the RP3D.