Immune checkpoint inhibitor treatment in PD-L1-negative gastroesophageal cancer tumors.

Abstract

e16062 Background: We aimed to investigate whether there is a subgroup of patients with gastroesophageal cancers who, despite having IHC-PD-L1 negative tumors, might still benefit from ICI treatment. Furthermore, the impact of ICI treatment on patients with tumors that are PD-L1 negative by IHC but exhibit high CD274 (PD-L1) expression remains undefined. Methods: 1,416 esophageal adenocarcinomas (EA), 486 esophageal squamous carcinomas (ES), 859 esophagogastric junction adenocarcinomas (EJA), and 1,613 gastric adenocarcinoma (GA) samples were analyzed using NGS of DNA (NextSeq, 592 genes and NovaSeq, WES) and RNA (NovaSeq, WTS) (Caris Life Sciences, Phx, AZ). PD-L1 IHC positivity was defined as > 1% CPS (Agilent's 22c3). Correlation between PD-L1 CPS and CD274 expression (transcripts per million – TPM) were assessed by Spearman’s coefficient. Tumors were divided into CD274-H (high expression) and CD274-L (low expression) cohorts, representing the top 25% and bottom 25% of expression levels, respectively. Real-world overall survival (OS) data were obtained from insurance claims records and analyzed using Cox proportional hazards with hazard ratios (HR) and log-rank tests. Results: Weak correlations were observed between PD-L1 CPS and CD274 expression in adenocarcinoma histology tumors (EA: 0.374, EJA: 0.358, GA: 0.387), while a stronger correlation was found in squamous tumors (ES: 0.537). Median CD274 expression was significantly higher in PD-L1+ compared to PD-L1- ES tumors (2.65-fold) and in EA (1.68-fold), EJA (1.92-fold), and GA (1.96-fold) tumors (p < 0.001). In PD-L1 IHC-negative ES, there was no association between CD274-H expression and OS (H 12.4 vs L 10.6 mo; HR 0.90, p = 0.48). However, in adenocarcinomas, CD274-H showed a slightly improved OS (12.8 vs 11.3 mo; HR 0.79, p < 0.05). CD274-H trended towards worse post-Carboplatin/paclitaxel (CP) OS (ES: 13.8 vs 18.2 mo; HR 1.60; p = 0.22; Adenocarcinoma: 18.2 vs 27.4 mo; HR 1.50, p = 0.19). Interestingly, CD274-H was associated with improved post-CP/nivolumab survival in ES (96.5 vs 28 mo; HR 0.32; p = 0.047), with a similar but not statistically significant pattern in Adenocarcinoma EGC (Not Reached vs 30.2 mo; HR 0.39, p = 0.23). Furthermore, in CD274-L GEC, there was no difference in post-treatment survival with the addition of Nivolumab to CP (Squamous: 30 vs 18.2 mo; HR 0.91, p = 0.83; Adenocarcinoma: 30.2 vs 27.4 mo; HR 1.14; p = 0.76). In contrast, CD274-H showed improved survival with the addition of Nivolumab (Squamous: 96.5 mo vs 13.8 mo; HR 0.15; p = 0.01; Adenocarcinoma: NR vs 18.2 mo; HR 0.30; p = 0.08). Conclusions: High CD274 expression was associated with improved survival when Nivolumab was added to chemotherapy in patients with PD-L1-negative tumors. Further investigation is needed to confirm the potential benefits of Nivolumab treatment in gastroesophageal cancer patients with tumors that are PD-L1-negative by IHC but exhibit high mRNA expression.