587. PD-L1 EXPRESSION AND CD8+ TUMOR-INFILTRATING LYMPHOCYTES CHANGES AFTER PREOPERATIVE CHEMORADIOTHERAPY IN ESOPHAGEAL SQUAMOUS CELL CARCINOMA

Abstract Background Neoadjuvant chemoradiotherapy (nCRT) has been established as a standard treatment for locally advanced esophageal squamous cell carcinoma (SqCC), but there are still insufficient research advances on the incorporation of immunologic agents. The aim of this study was to explore immune microenvironment changes before and after nCRT. Methods A total of 101 patients who underwent nCRT followed by radical surgery for esophageal SqCC in a single institution between 2005 and 2021 were analyzed. Pre-nCRT endoscopic biopsy and post-nCRT surgical specimen were evaluated using tissue microarray. Immunohistochemical staining for CD3, CD8, and PD-L1 were performed. Tumor-infiltrating lymphocytes (TIL) density were independently evaluated by blinded pathologist (total number of 2+ to 3+ cells/total area (mm2)). Results Compared to pre-nCRT biopsy, PD-L1 expression (8.7% vs. 14.0%, p<0.001) and TIL density (259.1 vs. 566.9, p<0.001) were significantly increased in surgical specimen after nCRT. When divided into groups according to nCRT response, post-nCRT TIL density (p=0.341), fold changes of TIL density (p=0.749), and PD-L1 expression (p=0.642) were not significantly different between ypCR (n=23) and non-ypCR group (n=78). In ypT0 group (n=36), post-nCRT TIL density was marginally higher than that of non-ypT0 group (404 vs. 259, p = 0.050). Conclusion Irrespective of clinical responses, PD-L1 expression and TIL density were both increased after nCRT. Our results could help the development of combination strategy of immunologic drugs and seek the possibility of an organ-saving strategy that will contribute to improving quality of life of patients.