Multiple Incidental Pancreatic Neuroendocrine Tumors in a Patient With Suspected Duodenal Papillary Adenocarcinoma: A Case Report.

Pancreatic neuroendocrine tumors (PNETs) are rare neoplasms that can mimic periampullary adenocarcinomas, presenting significant diagnostic challenges. Preoperative distinction is crucial due to the distinct prognostic and therapeutic implications of each entity. We report the case of a male patient with obstructive jaundice, whose initial investigation suggested duodenal papillary adenocarcinoma. Preoperative endoscopic biopsy was inconclusive for malignancy. Given the high clinical suspicion, the patient underwent duodenopancreatectomy. Anatomopathological examination of the surgical specimen unexpectedly revealed multiple implants of well-differentiated PNET (Grade G), without evidence of adenocarcinoma. This case illustrates the well-known limitation of endoscopic biopsy in periampullary tumors, which presents false-negative rates of up to a significant percentage. The final diagnosis of multiple Grade G PNETs, a rare condition frequently associated with genetic syndromes such as multiple endocrine neoplasia type 1, radically altered the patient's prognosis, which is significantly more favorable compared to papillary adenocarcinoma. Surgical resection remains an indispensable diagnostic and therapeutic tool in cases of biliary obstruction with high suspicion of malignancy, even with negative preoperative biopsies. The incidental finding of Grade G PNET reinforces the importance of complete histopathological analysis of the surgical specimen for adequate diagnosis, prognosis, and follow-up.