Validation of Immunoscore for Prognostic Stratification in HPV-associated Oropharyngeal Cancer: An International Multicenter Study

Purpose: Optimizing treatment in HPV-associated OPSCC remains challenging, as current TNM- and smoking-based risk stratification inadequately captures tumor biological heterogeneity, highlighting the need for more prognostic biomarkers. We report the first validation of the Immunoscore (IS) in HPV-associated OPSCC. Experimental Design: We analyzed 191 HPV-associated (p16⁺ and HPV DNA/RNA⁺) OPSCC patients from an international multicenter cohort (2015–2024), including a French monocentric retrospective training cohort (n = 48) and three validation cohorts: French monocentric retrospective (n = 48), French multicenter prospective (n = 50), and US multicenter retrospective (n = 45). IS quantified CD3⁺ and CD8⁺ densities in tumor cores and invasive margins, with cut-offs defined in the training cohort and validated across cohorts. Associations with disease-free survival (DFS), overall survival (OS), and time to recurrence (TTR) were assessed, alongside 3’RNA-seq and sequential immunofluorescence profiling. Results: Median age 65; 80% male; 74% smokers; 66% T1-2; 82% N0-1. IS-High patients had superior 3-year DFS across cohorts (all log-rank P < .05). Multivariable analysis identified IS-Low as the independent prognostic factor with the largest adjusted effect size for DFS (HR 9.03; 95% CI: 4.02-20.31; P < .001). The combined IS-clinical model showed better DFS prediction than the clinical-only model (C-index 0.82 vs 0.70; P < .0001). Similar results were observed for TTR and OS. IS-High tumors showed enriched lymphoid and myeloid populations, contrasting with immune-poor IS-Low tumors. Conclusions: IS outperformed clinical variables in prognostic performance. By identifying biologically distinct risk groups, IS may enable biomarker-guided, risk-adapted treatment strategies, including treatment de-escalation and intensification.