Background: Adjuvant BRAF/MEK inhibitors (BRAF/MEKi) and immunotherapy with anti-PD-1 have become the standard of care for resected high-risk stage III and IV melanoma, but a head-to-head comparison is lacking. In our earlier study, we compared adjuvant BRAF/MEKi and anti-PD-1 in a nationwide cohort in the Netherlands. However, the follow-up was too limited for overall survival (OS) analysis. We present an updated analysis including OS with extended follow-up. Methods: We included all resected high-risk stage III melanoma patients treated with first-line adjuvant BRAF/MEKi and anti-PD-1 from the Dutch Melanoma Treatment Registry from 2018-2023. We performed a propensity score matched outcome analysis of 1- and 2-year recurrence-free survival (RFS), distant metastasis-free survival (DMFS), and OS. Grade ≥ 3 toxicity rates and discontinuation rates due to toxicity were described. Results: In total, 225 BRAF/MEKi-treated patients and 729 anti-PD-1-treated patients were included. BRAF/MEKi-treated patients had lower disease stages (16.4% versus 10.2% stage IIIA disease; p=0.01) and more comorbidities (76.0% versus 63.8%; p<0.01) than anti-PD-1-treated patients. Median follow-up duration was 20.9 months. Two similar groups of 213 patients each were created by propensity score matching. Before matching, RFS and DMFS were significantly shorter in the anti-PD-1 treated patients, OS was not (Table). After matching, the 1- and 2-year RFS, DMFS and OS rates were not significantly different (Table). Toxicity data will be presented at the meeting. Conclusions: Our results suggest no significant differences in outcomes between adjuvant BRAF/MEKi and anti-PD-1 treatment in stage III melanoma.

DMFS = distant metastasis-free survival, OS = overall survival, RFS = recurrence-free survival.