Combined pancreatic grade 1 neuroendocrine tumour and ductal adenocarcinoma - MiNEN versus collision tumour: a rare surgical case report and diagnostic challenge.

A pancreatic combined Grade 1 neuroendocrine tumour (NET) and ductal adenocarcinoma (PDAC) - meeting morphological criteria for both mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN) and collision tumour - is exceptionally rare. We report a 68-year-old female with multifocal pancreatic cystic lesions, main pancreatic duct dilatation, and elevated CA 19-9, with imaging features consistent with intraductal papillary mucinous neoplasm. Following multidisciplinary review, total pancreatectomy with duodenectomy and Roux-en-Y reconstruction was performed. Histopathology revealed PDAC (65%) and a well-differentiated Grade 1 PanNET (35%), with the latter confirmed by diffuse positivity for Synaptophysin and Chromogranin A and Ki-67 < 1%. A co-existing simple mucinous cyst with high-grade dysplasia was also identified. Adjuvant XELOX chemotherapy was administered after the patient declined infusional FOLFOX. This case highlights the diagnostic challenge of distinguishing MiNEN from collision tumour in the absence of molecular clonality data, and adds to the sparse literature on combined pancreatic NET-PDAC neoplasms.