Biomarker-Stratified Efficacy of Immune Checkpoint Inhibitors in Locally Advanced Head and Neck Squamous Cell Carcinoma: A Systematic Review and Meta-Analysis of Randomized Trials

Introduction: The role of immune checkpoint inhibitors (ICIs) in locally advanced head and neck squamous cell carcinoma (LA HNSCC) remains uncertain, with randomized trials showing inconsistent results in heterogeneous populations. We conducted a systematic review of randomized trials evaluating ICI-based strategies in LA HNSCC, with outcomes stratified by PD-L1 expression, HPV/p16 status, and cisplatin eligibility to identify patient subgroups most likely to benefit from ICIs. Methods: MEDLINE, Cochrane, and EMBASE databases were systematically searched up to 10 January 2026. Randomized controlled trials (RCTs) evaluating ICIs in patients with LA HNSCC were included. The primary outcome was pooled time-to-event efficacy, including event-free survival (EFS), progression-free survival (PFS), and disease-free survival (DFS) as reported across trials. A generic inverse variance method was used to calculate the estimated pooled hazard ratio (HR) for PFS with 95% confidence interval (CI). Heterogeneity was assessed with Cochran’s Q test. Random effects model was applied. Results: A total of 3605 patients from seven phase II/III RCTs were included. In the overall population, no significant difference in EFS/PFS/DFS was observed between ICI and standard therapy (HR 0.90; 95% CI: 0.77–1.06; p = 0.20). However, in subgroup analyses stratified by PD-L1 expression, patients with PD-L1-positive tumors demonstrated improved PFS with ICIs compared with control (HR 0.78; 95% CI: 0.67–0.91; p < 0.0001). In contrast, PD-L1-negative tumors demonstrated inferior PFS in the ICIs arm (HR 1.31; 95% CI: 1.02–1.68; p = 0.03). No significant differences in PFS were observed based on HPV or p16 status. A subset analysis of cisplatin-eligible LA HNSCC trials evaluating the addition of ICIs to standard therapy showed a similar pattern. ICI use in PD-L1-positive patients demonstrated significantly improved PFS (HR 0.76; 95% CI: 0.63–0.92; p < 0.0001), while ICI use in PD-L1-negative patients demonstrated decreased PFS (HR 1.28; 95% CI: 0.99–1.66; p = 0.06). In cisplatin-ineligible populations, ICI regimens did not improve PFS compared with cetuximab plus RT. Conclusions: This study showed that although in the overall population there was no significant difference in EFS/PFS/DFS, in the PD-L1-positive subgroup, patients experienced significantly improved PFS with ICIs compared with control, while in the PD-L1-negative subgroup, patients demonstrated inferior PFS in the ICIs arm; these results were mirrored in the cisplatin-eligible subgroup.