The incidence of Epstein-Barr Virus-associated gastric cancer in an Irish population

236 Background: Gastric adenocarcinoma is the fourth most frequent cancer worldwide and the second leading cause of cancer deaths. According to The Cancer Genome Atlas (TCGA) 9% of gastric carcinomas are associated with Epstein-Barr Virus (EBV). EBV- associated gastric carcinoma (EBV-GC) has distinct clinicopathological features, with a marked lymphocytic infiltrate, a generally diffuse histological type and a better prognosis. The immune cell infiltration in EBV-GC suggests a role for immune checkpoint inhibition, which currently has modest activity in unselected gastric cancer. Methods: All cases of gastric or junctional adenocarcinoma diagnosed between Jan 2019 and March 2020 in Mater Misericordiae University Hospital (MMUH) and Jan 2017 and Jan 2019 in Cork University Hospital (CUH) were identified. Electronic medical records were retrospectively reviewed to collect demographic and clinicopathological data such as AJCC TNM stage, tumour subtype and grade, HER-2 status, MMR proficiency and EBV status as determined by EBV-encoded RNA in situ hybridization. Results: N = 103 cases of gastric or junctional adenocarcinoma were identified. 67 male, 36 female, median age 64.5 (range 34 – 95). 40/103 had undergone surgical resection. EBER-ISH was assessed in all patients. 8 of 103 (7.8%) patients showed EBV positivity. These cases were all male patients, median age 62 (range 51-73). The tumours were located as follows; 2 in the cardia, 5 in the body and 1 not documented. The specimens were graded as; 87.5% (7/8) tumours being poorly differentiated and 1/8 moderate to poorly differentiated. The tumour subtypes were specified as; 62.5% (5/8) diffuse, 12.5% (1/8) intestinal and 25% (2/8) mixed intestinal and diffuse. 5/8 patients were locally confined and underwent resection for N0 disease. 3/8 (37.5%) patients had metastatic disease. None of the 8 EBV-GC cases were identified as being HER-2 positive or MMR-deficient. Conclusions: EBV-GC accounted for 7.8% of all gastric cancers in two large tertiary referral centres in Ireland. 37.5% of these patients had metastatic disease. Given this frequency and a possible predictive role in selecting for immunotherapy we conclude that routine assessment of EBV status is feasible in advanced gastric cancer.