Combined PD-L1 expression and PD-1+ CD8 T cells to predict immunotherapy outcomes in esophageal squamous cell carcinoma.

4053 Background: Esophageal squamous cell carcinoma (ESCC), the predominant subtype of esophageal cancer in Asia, remains a challenging disease with poor prognosis due to frequent late-stage diagnoses. Immune checkpoint inhibitors (ICIs), particularly those targeting the PD-1/PD-L1 axis, have revolutionized cancer treatment but benefit only a subset of patients. The identification of robust predictive biomarkers is critical to enhance patient selection and optimize immunotherapy outcomes. In this study, we leveraged multiplex immunofluorescence to comprehensively evaluate the roles of PD-L1 and PD-1 expression, immune cell subsets, and clinical factors in predicting immunotherapy efficacy in ESCC. Methods: We analyzed baseline tumor samples from 147 ESCC patients treated with first-line ICIs using multiplex immunofluorescence to assess the expression of PD-1, PD-L1, CD4, CD8, CD20, and CD68. Patients were stratified by biomarker expression levels, with cut-off values determined through ROC curve analysis to calculate AUC. Survival outcomes were analyzed, and multivariate Cox regression identified independent predictors of progression-free survival (PFS) and overall survival (OS). Results: PD-L1 expression (HR 0.266, 95%CI 0.087-0.816, p = 0.021) and PD-1+CD8+ T cells (HR 2.694, 95%CI 1.162-6.246, p = 0.021) emerged as independent predictors of PFS. High PD-L1 expression was associated with superior outcomes (mPFS: 7.6 vs. 5.5 months), while elevated PD-1+CD8+ T cell infiltration correlated with poorer outcomes (mPFS: 6.0 vs. 7.2 months). Patients with a combination of high PD-L1 expression and low PD-1+CD8+ T cells demonstrated the best prognosis, with a median PFS of 8.5 months, whereas those with low PD-L1 expression and high PD-1+CD8+ T cells had the worst prognosis, with a mPFS of 3.5 months. Clinical stage (HR 1.570, 95%CI 1.059-2.327, p = 0.025), BMI (HR 0.935, 95%CI 0.883-0.990, p = 0.015), and CD8+ T cell density (HR 0.896, 95%CI 0.824-0.975, p = 0.011) were identified as independent predictors of OS. Conclusions: Our findings uncover the dual importance of PD-L1 expression and PD-1+CD8+ T cell infiltration as critical biomarkers for predicting PFS in ESCC patients undergoing ICIs. Moreover, clinical factors such as BMI, tumor stage, and intratumoral CD8+ T cell density significantly impact OS.