GAST and chronic atrophic gastritis: In humans, elevated serum gastrin levels are observed in patients with chronic atrophic gastritis due to achlorhydria-induced loss of negative feedback, and hypergastrinemia has been associated with increased risk of gastric neuroendocrine tumors and adenocarcinoma (Waldum and Mjønes, 2023; Waldum and Mjønes, 2020).