Invasive Gastric Adenocarcinoma Arising in a Giant Pedunculated Polyp Causing Intermittent Gastric Outlet Obstruction: A Case Report.

A 69-year-old woman with no significant medical or surgical history presented with a three-month history of epigastric pain, early postprandial vomiting, and dyspepsia. Thoracoabdominopelvic computed tomography showed marked esophageal and gastric stasis upstream of an endoluminal polypoid mass extending toward the duodenal bulb. Upper gastrointestinal endoscopy revealed an approximately 4-cm pedunculated polyp arising from the gastric body and intermittently prolapsing through the pylorus. Initial superficial biopsies showed inflammatory and ulcerative changes without evidence of malignancy. Endoscopic snare polypectomy was subsequently performed. Histopathological examination of the resected specimen revealed a moderately differentiated adenocarcinoma arising in a tubular adenoma containing both low- and high-grade dysplasia. The tumor invaded the submucosa to a depth of 2,400 µm, without lymphovascular invasion, perineural invasion, or tumor budding. Because the depth of submucosal invasion exceeded the criteria for curative endoscopic resection, subtotal gastrectomy with lymph node dissection was performed. No residual tumor was identified, and all 13 examined lymph nodes were negative for metastasis. This case illustrates a rare presentation of invasive gastric adenocarcinoma arising in a large pedunculated gastric adenoma and causing intermittent gastric outlet obstruction through pyloric prolapse. It emphasizes the limitations of superficial biopsies in suspicious polypoid lesions and the importance of complete histological assessment and multidisciplinary management after non-curative endoscopic resection.