Duodenal gastric-type neoplasm with uncertain malignant potential in a lipoma

The pathologic diagnosis of duodenal tumors is a developing field; however, its overview remains unclear. We describe a rare case of a duodenal gastric-type neoplasm in a 50-year-old woman. She visited her primary care doctor with complaints of upper abdominal pain, tarry stools, and shortness of breath on exertion. She was admitted owing to a stalked polyp with erosion and hemorrhage in the descending part of the duodenum. Endoscopic mucosal resection (EMR) was performed on the polyp. Histologically, the resected polyp was a lipomatous lesion in the submucosal layer, composed of mature adipose tissues. Scattered irregular lobules of Brunner's gland-like structures with well-preserved construction but mildly enlarged nuclei and occasional conspicuous nucleoli of the constituent cells were observed. The resection margin was negative. EMR findings of the duodenal polyp showed a gastric epithelial tumor within a lipoma, a rare histological type that has not been reported previously. This tumor may be classified as a "neoplasm with uncertain malignant potential" in a lipoma, an intermediate category between adenoma and invasive adenocarcinoma. There is no consensus on treatment, and careful follow-up is recommended. This is the first report of a duodenal gastric-type neoplasm with uncertain malignant potential in a lipoma.