A 69-year-old man undergoing long-term administration of a proton-pump inhibitor (PPI) underwent upper endoscopy, which found a small, whitish, flat lesion in the fundic gland (oxyntic) mucosa. The patient had never received treatment for Helicobacter pylori (Hp) infection, and diagnostic testing for Hp was negative, suggesting an Hp-naïve status. Two years later, the lesion appeared markedly enlarged and was endoscopically resected. Histological examination revealed a low-grade foveolar-type gastric adenoma (FGA), predominantly expressing MUC5AC by immunohistochemistry. Two years later, while PPI therapy was continued, three new flat lesions were found. These were endoscopically resected and histologically diagnosed as low-grade FGAs as before, suggesting that multiple metachronous tumors had developed in a short period of time during long-term PPI administration. A KRAS mutation and a CTNNB1 mutation were identified in the tumor. To our best knowledge, this is the first report of potentially PPI-associated multiple metachronous FGAs in an Hp-naïve patient. Here we report a case of multiple foveolar-type gastric adenomas with rapid metachronous recurrences during long-term use of a proton pump inhibitor in Helicobacter pylori-naïve patient.
