Gastric adenocarcinoma of fundic gland type arising from heterotopic gastric glands during a 19-year follow-up period.

A 73-year-old man with prior history of duodenal ulcer has been undergoing periodic upper gastrointestinal endoscopy since 1999. In 2017, a 25-mm submucosal tumor-like protrusion was detected in the lesser curvature of the upper stomach; histological examination of the lesion revealed gastric adenocarcinoma of fundic gland type. En bloc resection was achieved using endoscopic submucosal dissection. The patient was histopathologically diagnosed with gastric adenocarcinoma of fundic gland type arising from heterotopic gastric glands. Immunohistochemical staining was positive for MUC5AC, MUC6, pepsinogen I, and proton pump but negative for MUC2 and CD10. Moreover, the patient's Ki-67 labeling index score was extremely low. The presence of MUC5AC indicated that the tumor differentiated to the foveolar epithelium and fundic glands. Gastric adenocarcinoma of fundic gland type that differentiates to several directions has a higher malignant potential than the disease that differentiates to chief cells. A retrospective review of the patient's previous endoscopic examination revealed that the submucosal tumor-like protrusion existed since 2000; tumor size increased from 8 mm in 2000 to 25 mm in 2017. The present case is rare in that the carcinoma arose from heterotopic gastric glands. Moreover, the 19-year follow-up revealed that the tumor differentiated to the foveolar epithelium, considered as having high-grade malignancy.