Abstract CT021: Tumor-associated immune cell PD-L1 expression and peripheral immune profiling: Analyses from CheckMate 141

Introduction: In the phase 3 study CheckMate 141 (NCT02105636), patients with platinum-refractory head and neck squamous cell carcinoma treated with nivolumab (NIVO) had longer median overall survival (OS) (7.5 vs 5.1 months; P=0.01) and a higher objective response rate (all: 13.3 vs 5.8%; tumor PD-L1 ≥1%: 17 vs 1.6%) compared with investigator’s choice (IC) (Ferris et al. NEJM. 2016). This exploratory analysis evaluated the immune profile of patients from CheckMate 141, in context of tumor PD-L1 expression, and assessed the relationship with treatment (txt) outcomes. Methods: PD-L1 expression in tumor and tumor-associated immune cells (TAIC) was analyzed at baseline (n=252) and assessed for association with clinical outcome. Tumor PD-L1 expression was quantitatively assessed using Dako IHC 28-8 pharmDx assay. TAIC PD-L1 abundance (numerous/intermediate, rare) and location (intra/intra-peritumoral, peritumoral) were qualitatively assessed (unvalidated). Peripheral blood (n=36) at baseline and day 43 was assessed for immune cell biomarkers by flow cytometry and analyzed by 2-way ANOVA with Sidak’s multiple comparisons test correction. Results: Abundant PD-L1+ TAICs (numerous/intermediate) were associated with greater median OS with NIVO vs IC in tumors with PD-L1 ≥1% (abundant: 8.7 vs 4.4 months, hazard ratio [HR] and 95% CI 0.44 [0.27, 0.71] and rare: 6.7 vs 4.9 months, HR 0.88 [0.42, 1.86]) and PD-L1