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Background Gastric cancer with peritoneal metastases carries a median survival of only 3-7 months without treatment. Meanwhile, cancers arising from the oesophago-gastric junction (OGJ) are rapidly increasing in incidence in the Western population and are also commonly associated with peritoneal metastases. In order to measure the efficacy of emerging modes of treatment for peritoneal disease, it is essential to describe the treatments patients currently receive and the impact of these on survival – data for which is poorly described in the literature and lacking in the UK setting. Methods This was a single hospital-based retrospective cohort study covering the period from March 2012 to January 2020 at a tertiary referral centre. 50 patients were identified from multidisciplinary team (MDT) meeting records receiving a diagnosis of gastric adenocarcinoma with isolated peritoneal disease. 31 patients were identified receiving a diagnosis of true (Siewert II or III) junctional adenocarcinoma with isolated peritoneal disease. We calculated median survival time for all patients and also by treatment modality. Results Mean age of patients with gastric adenocarcinoma and isolated peritoneal disease was 71 years (range 44-90). Overall median survival was 6.6 months (IQR 2.4-19.3). Median survival was 11.2 months (IQR 3.7-21.5) for patients receiving systemic chemotherapy (n = 26) and 2.4 months (IQR 1.2-5.1) for patients receiving best supportive care alone (n = 15). Mean age of patients with junctional adenocarcinomas and isolated peritoneal disease was 70 years (range 37-89). Overall median survival was 7 months (IQR 3-19). Median survival was 10.5 months (IQR 6.5-20.5) for patients receiving systemic chemotherapy (n = 20) and 3.5 months (IQR 2-6) for patients receiving best supportive care alone (n = 6). Conclusions Our results demonstrate the poor prognosis of both gastric and oesophagogastric cancer patients with isolated peritoneal disease. Prognosis figures are comparable between the two cancer types. Findings are in line with previous studies performed outside the UK which have shown that available treatments extend survival by no more than 3-9 months, highlighting the desperate need for new treatment modalities.