Ectopic gastric squamous metaplasia with concomitant well-differentiated adenocarcinoma: a case report

BACKGROUND: Gastric squamous metaplasia is a rare condition whose clinical significance and malignant potential remain unclear. Most reported cases are located in the cardia and are continuous with the esophageal squamous epithelium. Ectopic gastric squamous metaplasia, defined as lesions discontinuous from the esophagus, is exceedingly rare, and its association with gastric neoplasms has not been well characterized. CASE PRESENTATION: An 81-year-old woman with a history of Helicobacter pylori eradication underwent esophagogastroduodenoscopy for gastric cancer screening. A 20-mm discolored, slightly depressed lesion was identified on the greater curvature of the upper gastric body. The lesion was discontinuous from the esophageal mucosa and appeared as an iodine-unstained area. Magnifying endoscopy with narrow-band imaging revealed intrapapillary capillary loop-like vascular dilation with background coloration. Biopsy specimens suggested squamous metaplasia with reactive atypia, and en bloc resection was performed by endoscopic submucosal dissection. Postoperative histopathological examination identified mature stratified squamous epithelium consistent with gastric squamous metaplasia, and incidentally identified a well-differentiated adenocarcinoma confined to the mucosa adjacent to the metaplastic lesion without lymphovascular invasion. Immunohistochemical analysis revealed a linear arrangement of p63-positive cells along the basal layer of the metaplastic epithelium with a subset of Ki-67-positive cells indicating proliferative activity at the basal layer. p53 expression showed a wild-type pattern. CONCLUSIONS: We report an extremely rare case of ectopic gastric squamous metaplasia associated with well-differentiated adenocarcinoma. Although a direct histogenetic relationship between the two lesions remains uncertain, their coexistence raises important considerations regarding the pathogenesis of gastric squamous metaplasia and its potential clinical significance. The immunohistochemical findings may support a possible role of competitive epithelial replacement in the development of gastric squamous metaplasia. Careful endoscopic and histopathological evaluation is warranted when this rare lesion is encountered.