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Case Report
Mixed adenoma–well-differentiated neuroendocrine tumor of the major duodenal papilla: Case report with review of literature
1 Assistant, Department of Human Pathology, School of Medicine, Juntendo University, Tokyo, Japan
2 Associate Professor, Department of Human Pathology, School of Medicine, Juntendo University, Japan
3 Associate Professor, Department of Hepatobiliary-Pancreatic Surgery, School of Medicine, Juntendo University, Tokyo, Japan
4 Assistant Professor, Department of Gastroenterology, School of Medicine, Juntendo University, Tokyo, Japan
5 Professor, Department of Human Pathology, School of Medicine, Juntendo University, Tokyo, Japan
Address correspondence to:
Yuki Fukumura
Department of Human Pathology, School of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421,
Japan
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Article ID: 100099Z11YK2026
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Kubota Y, Fukumura Y, Hirata Y, Takasaki Y, Yao T. Mixed adenoma–well-differentiated neuroendocrine tumor of the major duodenal papilla: Case report with review of literature. J Case Rep Images Pathol 2026;12(1):10–15.ABSTRACT
Introduction: Mixed adenoma–well-differentiated neuroendocrine tumor (MANET) is a recently introduced tumor entity, composed of an adenoma and a well-differentiated neuroendocrine tumor. It occurs infrequently in the colorectum, is very rare in the duodenum, and no case arising from the major duodenal papilla has been reported to date.
Case Report: We describe an extremely rare case of MANET arising from the major duodenal papilla in a woman in her 80s. The patient underwent endoscopic examination for abnormal liver function tests, which revealed a hypervascular, elevated lesion at the major duodenal papilla. Because ampullary carcinoma was suspected, subtotal stomach-preserving pancreaticoduodenectomy was performed. The 30 × 6 mm whitish tumor centered on the major papilla was histologically composed of three components: a pure adenomatous component, a pure neuroendocrine tumor component, and a mixed adenomatous-neuroendocrine component. The adenomatous component was predominantly high-grade, and the neuroendocrine component corresponded to grade 2. “Budding-off” and “ductuloinsular complex” patterns were frequently observed in the mixed component. Immunohistochemically, the neuroendocrine component was positive for serotonin and CDX2 in addition to neuroendocrine markers. Six months after surgery, the patient developed multiple metachronous liver metastases derived from the neuroendocrine component, and several metastatic foci were histologically diagnosed as grade 3 neuroendocrine tumor.
Conclusion: Although rare, considering the possibility of MANET in the major duodenal papilla is essential to avoid misdiagnosis as neuroendocrine carcinoma or adenocarcinoma. In this paper, we summarize the clinicopathological features of MANET based on a review of literature and discuss issues requiring further investigation.
Keywords: Major duodenal papilla, Mixed adenoma–well-differentiated neuroendocrine tumor, Mixed neuroendocrine–non-neuroendocrine neoplasm
SUPPORTING INFORMATION
Author Contributions
Yasuhiro Kubota - Conception of the work, Design of the work, Acquisition of data, Analysis of data, Drafting the work, Revising the work critically for important intellectual content, Final approval of the version to be published, Agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Yuki Fukumura - Conception of the work, Design of the work, Acquisition of data, Analysis of data, Drafting the work, Revising the work critically for important intellectual content, Final approval of the version to be published, Agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Yoshihiro Hirata - Acquisition of data, Revising the work critically for important intellectual content, Final approval of the version to be published, Agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Yusuke Takasaki - Acquisition of data, Revising the work critically for important intellectual content, Final approval of the version to be published, Agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Takashi Yao - Revising the work critically for important intellectual content, Final approval of the version to be published, Agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Guarantor of SubmissionThe corresponding author is the guarantor of submission.
Source of SupportNone
Consent StatementWritten informed consent was obtained from the patient for publication of this article.
Data AvailabilityAll relevant data are within the paper and its Supporting Information files.
Conflict of InterestAuthors declare no conflict of interest.
Copyright© 2026 Yasuhiro Kubota et al. This article is distributed under the terms of Creative Commons Attribution License which permits unrestricted use, distribution and reproduction in any medium provided the original author(s) and original publisher are properly credited. Please see the copyright policy on the journal website for more information.
