LAUSR

A man in his sixties was referred to our hospital for endoscopic resection after he was diagnosed with a 10-mm erythematous protrusion in the duodenal bulb (Fig. 1a). The surface of the protruding area was smooth and resembled a submucosal tumor (SMT) on white-light imaging. Magnifying narrow-band imaging (ME-NBI) revealed irregular microvascular structures and a closed-type surface structure (defined as a circular, polygonal, or oval-shaped mucosal structure) with deposition of a white opaque substance (Fig. 1b). Endoscopic ultrasonography (EUS) revealed a low-echoic area invading the muscle layer (Fig. 1c). The biopsy showed adenocarcinoma. The lesion was only 10 mm in diameter but was suspected to have invaded the muscle layer. Based on the ME-NBI findings, the lesion was thought to have a gastric phenotype. The patient underwent laparoscopic distal gastrectomy with lymph node dissection. Pathological examination of the resected specimen revealed a moderately differentiated adenocarcinoma invading the muscle layer and lymphatic vessels without lymph node metastasis. The resected lesion measured 11 mm in diameter. Immunohistochemistry indicated that the cancer cells were positively stained for mucin 5 AC and mucin 6 and negatively stained for mucin 2, confirming a gastric phenotype (Fig. 2). The cancer cells were partially positively stained for synaptophysin but not enough to be considered a neuroendocrine tumor. Cancer cells were exposed on the surface of the lesions. The patient developed local recurrence and liver metastasis 8 months after surgery and was treated with modified fluorouracil plus oxaliplatin (mFOLFOX6) therapy as the first-line regimen, followed by irinotecan as the second-line regimen. The patient died 16 months postoperatively. Duodenal neoplasms with gastric phenotypes commonly occur in the proximal duodenum and show increased malignant potential compared with intestinal phenotypes. In addition, for duodenal neoplasms, lesion size larger than 10 mm are predictors of duodenal adenocarcinoma. We perform underwater or conventional endoscopic mucosal resection (EMR) for small duodenal neoplasms of gastric type if intramucosal cancer is suspected. In this case, the lesion was relatively small in size, which rendered it dangerous to resect through cold snare polypectomy (CSP) without an appropriate preoperative diagnosis. CSP is associated with a shallower resection depth compared with EMR. EUS is useful for assessing the invasion depth of tumors. For lesions with an SMT-like morphology, EUS may be useful for obtaining subepithelial information. It is important to recognize that duodenal neoplasms with gastric phenotypes have a poor prognosis, even if they are small. In this case report, we described a rare case of advanced duodenal carcinoma measuring 10 mm in diameter with a gastric phenotype. An appropriate treatment plan should be formulated according to the histological phenotype and progression of the disease, as well as the fact that duodenal tumors with gastric phenotypes have a high malignant potential.