Neuroendocrine tumors of the gastrointestinal and pancreatobiliary tracts

Abstract

Significant improvements have taken place in the classification of neuroendocrine neoplasms in the past decade. These are now regarded in three entirely separate categories: (I) neuroendocrine tumors (NETs) are by definition well differentiated(II) neuroendocrine carcinomas, which are poorly differentiated (NEC)(III) other neoplasms that have neuroendocrine differentiation or a distinct neuroendocrine component. NETs are graded into 3, based on the proliferative activity, mostly based on the Ki-67 index. NECs are by definition high grade. Neuroendocrine neoplasms with well differentiated morphology but Ki-67 >20% are now regarded as NET Grade 3 (G3). They have been shown to have a prognosis significantly worse than lesser grade NETs but still incomparably better than frank NECsthe latter typically has Ki-67 >50% (often much higher) and require platinum-based chemotherapy. For low grade (G1/G2) NETs, more refined criteria to further prognosticate this group are needed. Morphologic variants being recognized may bring new perspectives to this group. © 2022 Elsevier Inc. All rights reserved.