A 72-year-old man visited our hospital for epigastric pain. Upper gastrointestinal endoscopy showed a 30-mm elevated lesion with a shallow ulcer at the superior duodenal angulus, and a biopsy revealed a duodenal neoplasm of a gastric phenotype (DNGP). In a preoperative examination, it was difficult to determine if the lesion was benign or malignant. Therefore, we performed laparoscopy and endoscopy cooperative surgery (LECS) as diagnostic treatment. The postoperative course was smooth. The final pathological diagnosis was well to moderately differentiated adenocarcinoma, gastric phenotype. There are various treatments with different surgical stress for a descending duodenal tumor, and the treatment should be selected based on individual tumor progression and malignant potential. LECS for duodenal lesions is minimally invasive and safer than endoscopic treatment alone. It is often difficult to assess the malignant potential of DNGP preoperatively. LECS may be useful as diagnostic treatment for these tumors, as illustrated in the case reported here.
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