Background: Treatment-resistant melanoma remains a significant clinical challenge despite advances in immunotherapy. Combination approaches targeting multiple immune checkpoints have shown promise in preclinical studies but require rigorous clinical evaluation.

Methods: We conducted a multicenter, randomized, double-blind Phase II trial enrolling 312 patients with advanced melanoma who had progressed on prior anti-PD-1 therapy. Patients were randomized 1:1:1 to receive: (A) nivolumab plus ipilimumab, (B) nivolumab plus relatlimab, or (C) nivolumab plus experimental agent XYZ-4821. The primary endpoint was progression-free survival (PFS); secondary endpoints included overall survival (OS), objective response rate (ORR), and safety.

Results: At median follow-up of 18.3 months, median PFS was 4.2 months (arm A), 5.8 months (arm B), and 8.1 months (arm C). The combination of nivolumab plus XYZ-4821 demonstrated superior PFS compared to nivolumab plus ipilimumab (HR 0.62, 95% CI 0.44-0.87, p=0.006). Grade 3-4 treatment-related adverse events occurred in 42%, 28%, and 31% of patients in arms A, B, and C, respectively.

Conclusions: The novel combination of nivolumab plus XYZ-4821 showed improved efficacy with a manageable safety profile in treatment-resistant melanoma, warranting further investigation in Phase III trials.