# Mixed neuroendocrine-non-neuroendocrine neoplasms (MiNEN) in the non-ampullary region of the duodenum: a case report

## TL;DR

This case report describes a rare mixed neuroendocrine tumor in the duodenum with a poor prognosis.

## Contribution

The report presents a unique case of MiNEN in the non-ampullary duodenum with detailed clinical and pathological findings.

## Key findings

- The tumor was composed of neuroendocrine carcinoma and adenocarcinoma components.
- The patient developed peritoneal dissemination and bone metastasis within 5 months.
- The pathological diagnosis was MiNEN with a pStageIIIb classification.

## Abstract

Mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs), a very rare form of neuroendocrine neoplasm (NEN), are associated with poor prognosis. Herein, we present a rare case of duodenal MiNEN composed of neuroendocrine carcinoma (NEC) and adenocarcinoma in a non-ampullary lesion. A 70-year-old male referred to our hospital was found to have duodenal perforation with a tumor in the 2nd duodenal portion based on computed tomography. Biopsy revealed a poorly differentiated adenocarcinoma. Three weeks following emergency surgery for the perforation, pancreaticoduodenectomy of the duodenal tumor was performed. The resected specimen comprised a 45 × 35-mm protruding and circumferential tumor extracted from the 2nd portion, with no involvement of the papilla of Vater. Histopathological examination revealed coexisting poorly differentiated adenocarcinoma and NEC components. The final pathological diagnosis was MiNEN (por2 > sig + NEC). TNM: pT4b (SE), pN2, M0, pStageIIIb. The postoperative course was uneventful, developing peritoneal dissemination and multiple bone metastasis after 5 months, with death 7 months postoperatively.