Abstract 6144: Novel M2 macrophage gene signature as a biomarker of poor outcomes independent of TNM stage in peritoneal liquid biopsy of gastric cancer patients
Authors: Sullivan Kevin M. , Li Haiqing , Mahuron Kelly , Yuan Yate-Ching , Chao Joseph , Paz Benjamin , Han Haiyong , Fong Yuman , Woo Yanghee 
Published: June 2022

Abstract
Introduction: The infiltration or density of immunosuppressive or M2-macrophages has been correlated with worse prognosis in gastric cancer (GC). We hypothesized that a highly polarized transcriptional phenotype of M2 macrophages would be prognostic if detected in primary and peritoneal fluid samples of GC.
Methods: We derived a novel transcriptomic gene signature (MRC1, MS4A4A, CD36, CCL13, CCL18, CCL23, SLC38A6, FGL2, FN1, MAF) from published highly differentially expressed M2 genes that were identified from peripheral blood. We also evaluated a M1 signature (CCR7, IL2RA, CXCL11, CCL19, CXCL10, PLA1A, PTX3) and T cell cytolytic signature (GZMA, GZMB, GZMH, GZMM, PRF1). In primary GC, we used the UCSC Xena tool to analyze the TCGA Stomach Cancer cohort and compared transcriptional signature expression to histologic subtype and pathologic stage. We used log-rank test to compare Kaplan-Meier curves of overall survival (OS) and disease-free interval (DFI) for high versus low signature expression. In our institutional cohort consisting of GC patients with a range of T and N stages as well as with and without metastatic disease (n=28), we evaluated peritoneal fluid samples using single cell RNA sequencing for high and low signature expression in CD68+CD163+ monocytes and used log-rank test to compare OS.
Results: A total of 341 TCGA entries of primary GC were included. High expression of the M2 signature in GC was associated with diffuse- and mucinous-type adenocarcinoma, compared to tubular- and papillary-type adenocarcinoma (p&lt;0.001). High M2 signature expression was associated with later stage (Stage II or above) compared to early-stage GC (stage I) (p=0.02). Low M2 signature was associated with significantly improved 5-year OS (p=0.03) and DFI (p=0.04). M1 signature and T cell cytolytic signature were not associated with stage, OS, or DFI in primary GC. In GC peritoneal fluid samples, we identified patients with high (n=15) and low (n=13) signature expression in M2 cells. Independent of TNM-stage, high M2 signature expression in CD68+CD163+ cells within the peritoneal fluid of GC patients was associated with worse OS (median OS not reached at 30 months for low signature expression and 5.5 months for high expression, hazard ratio 2.82, p=0.048).
Conclusions: Our study validates a unique M2-associated transcriptomic gene signature as a biomarker of poor outcomes in both primary gastric tumors and peritoneal fluid of GC patients. Because both endoscopic biopsy and laparoscopy with peritoneal fluid collection are part of the standard workup for locoregional GC, an ubiquitous immune signature detected in primary tumor and peritoneal fluid of patients across TNM stages may serve as a clinically valuable indicator of an immunosuppressive patient state associated with poor survival.
Citation Format: Kevin M. Sullivan, Haiqing Li, Kelly Mahuron, Yate-Ching Yuan, Joseph Chao, Benjamin Paz, Haiyong Han, Yuman Fong, Yanghee Woo. Novel M2 macrophage gene signature as a biomarker of poor outcomes independent of TNM stage in peritoneal liquid biopsy of gastric cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6144.