A male in his eighties was endoscopically diagnosed with a gastric adenoma 11 years ago. His yearly follow-up consultations were unremarkable. Four years ago, he underwent H. pylori eradication. One year later, the lesions reportedly shrank. Two years later, the lesion enlarged and exhibited morphological changes. A malignancy was suspected, and endoscopic treatment was recommended. However, the patient refused. One year later, the lesion was further enlarged and deformed. Submucosal invasion was suspected. Surgery was performed, and the final diagnosis was an adenocarcinoma, pT1b (SM2).

This case highlighted the malignant transformation of gastric adenoma over time.