Abstract
Primary small bowel tumors are uncommon and usually carry a poor prognosis. Adenocarcinoma is the predominant histological type while lymphoma is far less common. Small bowel diffuse large B-cell lymphoma (DLBCL) can mimic adenocarcinoma; thus, the distinction can be challenging before tissue examination is performed. Bowel obstruction, as well as peritoneal involvement, are often seen in gastrointestinal (GI) adenocarcinoma cases; however, these features are extremely uncommon with GI lymphomas. Herein, the authors report an unusual case of an obstructing duodenal mass with peritoneal involvement, which was highly suspicious for an advanced duodenal adenocarcinoma. Surprisingly, sampling of the tumor revealed a diffuse large B-cell lymphoma.