Duodenal Adenocarcinoma with a Gastric Phenotype Demonstrating a Rapidly Progressive Course

We herein report a rare case of duodenal adenocarcinoma with a rapidly progressive course. Esophagogastroduodenoscopy revealed Brunner's gland hyperplasia in the bulbs of the duodenum three years prior to this presentation. Two years earlier, gastric foveolar metaplasia had been observed in the bulbs. One year earlier, the lesion had increased slightly in size. At this time, the lesion had markedly increased in size, and the duodenum was circumferentially stenotic due to the mass. Pathologically, he was diagnosed with duodenal adenocarcinoma with a gastric-dominant immunophenotype and he died two months later. Although extremely rare, we should keep in mind that duodenal tumors with a gastric phenotype may sometimes progress rapidly within a short period of time.