S6269 Bones in the Belly: A Case of Osseous Metaplasia in the Stomach

Introduction: Osseous metaplasia, a rare histologic phenomenon within the gastrointestinal tract, is predominantly described in colorectal lesions. Reports estimate fewer than 5 cases among 2,000 colorectal cancers, making gastric involvement scarce. The proposed mechanism involves chronic inflammation triggering mesenchymal cell differentiation into osteoblasts via cytokines and bone morphogenic proteins. The following case of osseous metaplasia was identified within a gastric hyperplastic polyp in a patient with chronic negative-H. pylori gastritis. Case Description/Methods: A 46-year-old woman with a history of gastroesophageal reflux disease, chronic right upper quadrant pain, polycystic ovarian syndrome, thyroid disease, obesity, fatty liver, and gastric polyps reported persistent abdominal discomfort. Abdominal imaging showed mild hepatomegaly and steatosis, otherwise unremarkable. However, upper gastrointestinal series revealed an irregularity in the gastric fundus. Furthermore, during endoscopy, the anomaly was further described as severe antral gastritis with presence of multiple polyps; 2 inflammatory polyps of 0.4 cm and 1.2 cm. Histology revealed foveolar hyperplasia, erosion, and osseous metaplasia, within a hyperplastic polyp; H. pylori negative. She was started on vonoprazan and sucralfate due to proton pump inhibitor intolerance. Discussion: Gastric hyperplastic polyps are often incidental and benign but merit removal when exceeding 1 cm due to potential for neoplastic transformation. The presence of osseous metaplasia adds diagnostic complexity. Though benign, osseous metaplasia is considered a reactive process linked to long-term mucosal injury, inflammation, or ischemia. In the absence of H. pylori or surgery, chronic gastritis may still trigger this rare stromal transformation. Osseous metaplasia has predominantly been reported in males and colorectal sites, making this case—woman, gastric, H. pylori-negative—highly atypical. While no immediate malignant risk is associated, its presence may reflect disordered tissue repair and warrants close monitoring. This case reinforces the need to biopsy and histologically assess all polyps >1 cm, even when endoscopically benign. More broadly, it raises the possibility that chronic inflammation alone may drive metaplastic processes, urging clinicians to lower thresholds for intervention and consider histologic changes as markers of underlying mucosal instability.