Efficacy and Safety of PD-1 Inhibitor-Based Regimens in Patients with Melanoma: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Programmed death-1 (PD-1) inhibitors have significantly improved survival outcomes in melanoma; however, questions persist regarding comparative efficacy across regimens and the predictive value of PD-L1 expression as a biomarker. We therefore performed a meta-analysis evaluating outcomes according to PD-L1 expression status using the most recent follow-up data from each study. Methods: A systematic search was conducted in PubMed, Cochrane and ClinicalTrials.gov from 1 January 2010 to 1 April 2025 for phase II and III randomized clinical trials (RCTs) investigating PD-1 inhibitors as monotherapy or combined with other immune checkpoint inhibitors (ICIs) or targeted therapy in the adjuvant/metastatic setting. Pooled estimates were calculated with random-effects models, and risk of bias was assessed using the Cochrane RoB 2 tool. The present meta-analysis was performed following PRISMA guidelines and was registered in PROSPERO (ID: CRD420251090090). Results: Fifteen RCTs including 9979 patients were included. In the overall analysis, PD-1 inhibitors were associated with significantly improved overall survival (OS, HR = 0.75, 95% CI: 0.66–0.86) compared with control treatments. In the unresectable or metastatic setting, progression-free survival (PFS) was also significantly improved (HR = 0.61, 95% CI: 0.49–0.76). Survival benefits were observed in both PD-L1-positive and PD-L1-negative tumors, with improved PFS in PD-L1-positive (HR = 0.63, 95% CI: 0.48–0.83) and PD-L1-negative patients (HR = 0.58, 95% CI: 0.44–0.77), as well as improved OS in PD-L1-positive (HR = 0.69, 95% CI: 0.59–0.80) and PD-L1-negative patients (HR = 0.79, 95% CI: 0.67–0.93), without evidence of effect modification by PD-L1 expression. PD-1 inhibitor-based regimens were not associated with a statistically significant increase in grade 3–4 treatment-related adverse events (RR = 1.13, 95% CI: 0.71–1.79); however, heterogeneity was substantial (I2 = 96.0%). Conclusions: PD-1 inhibitor-based therapies significantly improve survival outcomes in advanced melanoma across PD-L1 subgroups. No clear evidence of differential treatment benefit according to PD-L1 expression was observed, suggesting limited utility as a standalone predictive biomarker. Further studies integrating molecular and immune profiling are warranted to optimize individualized treatment selection.