Intratumoral immune landscape changes after neoadjuvant chemoradiation in esophageal cancer.

443 Background: Neoadjuvant chemoradiation (nCRT) remains a standard of care in esophageal cancer. Although adjuvant Nivolumab improves progression-free survival (PFS), 5-year overall survival (OS) remains suboptimal. It is uncertain if PDL1 expression is a useful predictive biomarker in this setting. This study prospectively evaluated intratumoral immune changes after nCRT and their associations with clinical outcomes. Methods: All patients were treated with the CROSS regimen (41.4Gy in 23 fractions with weekly paclitaxel & carboplatin) followed by surgery. Multiplex immunofluorescence was performed on paired pre-CRT and post-CRT FFPE sections, staining for CK, CD3, CD8, CD68, FOXP3 and PDL1. Images were captured using Zeiss Axioscan 7 slide scanner and analyzed by a pathologist using HALO v3.6 software. The average percentage staining was calculated. Pathological tumor response was centrally reviewed. Data were presented as median (IQR). Changes in the immune cell densities before and after nCRT were compared using Wilcoxon signed-rank test. Locoregional recurrence-free survival (LRRFS), PFS and OS were defined from time of diagnosis. Univariate Cox regression analysis was used to assess the effects of immune cell densities on survival outcomes. A p