Abstract 65: Differential impacts of PD-L1 expression in tumor vs. stroma on survival in esophageal squamous cell carcinoma

Abstract Background: Esophageal squamous cell carcinoma (ESCC) has high incidence and recurrence rates, particularly in advanced stages. While the combined positive score (CPS) and tumor proportional score (TPS) are standard benchmarks for PD-L1 assessment in ESCCs, they face challenges such as reliance on subjective human interpretation and the uncertain clinical significance of strong staining intensities. Our study utilizes H-scores for PD-L1 expression and separates analysis of tumor and stroma, providing additional layers of information that complement current methods and contribute to a more comprehensive understanding of the role of PD-L1 in ESCC. Methods: This retrospective single-center cohort analysis involved 194 cases of ESCC who underwent surgical resection. We performed a comprehensive evaluation of PD-L1 expression within the tumor and stroma using whole slide images (WSI). QuPath image analysis software was used to classify regions as tumor or stroma and quantify the PD-L1 expression H-score. Results: Using optimal H-score cutoffs determined from the minimum P-value method, the Kaplan-Meier survival analysis showed that higher PD-L1 expression was significantly linked with better post-operative survival across all compartments. This correlation was most pronounced in the stroma (P<0.001). However, in multivariate Cox regression analysis, only high tumoral PD-L1 expression emerged as an independent predictor of favorable prognosis (HR=0.47, 95% CI: 0.27-0.81, P=0.007). The non-significant contribution of stromal PD-L1 in this model could be attributed to its association with advanced pT and pN stages, and the presence of lymphatic and venous invasion (P<0.001, respectively). Interestingly, stromal PD-L1 expression was associated with a longer duration of cytotoxic chemotherapy (cutoff 8 months, Median H-score 98.28 vs 55.24, P=0.026), but no significant correlation was observed with the duration of immune checkpoint inhibitor treatment. Conclusions: The study underscores the complex role of PD-L1 in ESCC, with tumoral PD-L1 expression emerging as an independent prognostic factor, and stromal PD-L1 expression found to be related with tumor progression and the duration of cytotoxic chemotherapy response. Citation Format: Tomohiro Murakami, Satoru Furuhashi, Yuuki Sakai, Kenichi Sekimori, Ryoma Haneda, Eisuke Booka, Tomohiro Matsumoto, Hirotoshi Kikuchi, Yoshihiro Hiramatsu, Hiroya Takeuchi. Differential impacts of PD-L1 expression in tumor vs. stroma on survival in esophageal squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 65.