AGA Institute Acta Medica Okayama 15423565 20 2 2020 Gastric Adenocarcinoma and Proximal Polyposis of the Stomach Occurring With Ball Valve Syndrome e12 e13 EN Soichiro Ako Department of Gastroenterology and Hepatology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences Seiji Kawano Department of Gastroenterology and Hepatology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences Hiroyuki Okada Department of Gastroenterology and Hepatology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences No potential conflict of interest relevant to this article was reported.