ABSTRACT
Gastropancreatic neuroendocrine tumors (GEP-PanNETs) are epithelial neoplasms with predominant neuroendocrine differentiation that arise from the diffuse neuroendocrine cells in the gastrointestinal tract and the pancreas [1]. Although pancreatic neuroendocrine tumors (PanNETs) share similar histologic features with neuroendocrine tumors of the gastrointestinal tract (GEPs), it has become increasingly evident that they differ in molecular pathogenesis, clinical behavior, and responsiveness to certain therapies [2]. Since Oberndorfer first coined the term carcinoid tumor more than a century ago [3], a variety of nomenclatures have been proposed for this entity, such as “islet cell tumor,” “endocrine tumor or neoplasm,” “neuroendocrine tumor or neoplasm,” and “endocrine or neuroendocrine carcinoma,” which has caused great confusion clinically [4, 5]. The term islet cell tumors has been disparaged because evidence suggests that PanNETs arise from the pluripotent cells among the acinar–ductal cells of the pancreas, and also, PanNETs produce hormones not normally found in normal islet cells [6]. In 2010, the World Health Organization (WHO), together with the European Neuroendocrine Tumor Society (ENETS), the American Joint Committee on Cancer (AJCC), and the North American Neuroendocrine Tumor Society (NANETS), made great efforts to standardize the nomenclature, developed guidelines for PanNETs, and recommended a minimal data set for pathologic reports [1, 4, 7]. It was also agreed by a panel of experts that the terms endocrine and neuroendocrine are essentially synonymous, and that tumor and neoplasm can be used interchangeably [4, 8]. In the 2010 WHO classification system, PanNETs are separated into well-differentiated and poorly differentiated categories. The term carcinoma is reserved only for poorly differentiated pancreatic neuroendocrine carcinomas (PDPanNECs), consisting of small cell carcinoma and large cell neuroendocrine carcinoma.
