Incidental histological diagnosis of small pancreatic neuroendocrine tumors: are we underestimating their incidence?

Abstract

Background: The annual incidence of pancreatic neuroendocrine tumors (PanNET) has been estimated to be around 0.8/100,000 inhabitants. Aim of the study was to determine the frequency of incidental histological diagnosis of PanNET during pancreatic specimen evaluation for other neoplasms. Method: We retrospectively reviewed 1023 histopathological examinations of pancreatic specimens performed by three different pathologists in 3 high-volume centers in Italy. Preoperative evaluations and surgical procedures were performed directly or under the supervision of a single surgeon. All the cases with a main pathological diagnosis of PanNET were excluded. Results: An incidental associated diagnosis of PanNET was made in 38 specimens (4%). NET was the most frequent (57%) type of associated neoplasm followed by intraductal mucinous neoplasm (IPMN) (16%). Among those 38 cases, 29 (76%) had a largest diameter < 5 mm (microadenoma). 16 out of 38 incidental PanNET were classified as nonfunctioning (42%) whereas other 7 cases (18%) were classified as glucagonomas. A median value Ki67 of 1% was measured in 9 incidental PanNET. Patients with incidental PanNET were significantly older (median age: 69 years versus 65.5 years, P=0.003). There was no association between incidental diagnosis of PanNET and gender, operation, and main histological diagnosis. When excluding microadenomas, the median age between patients with incidental PanNET (n=9) and the remaining patients was no statistically different (median age 64 years versus 65.5 years, P>0.05). Conclusion: The frequency of incidental histological diagnosis of PanNETs is considerably high suggesting that their real incidence is probably underestimated.