ABSTRACT
The gastroenteropancreatic (GEP) system is a site of a wide variety of neoplasms. Neuroendocrine tumors (NETs) comprise a small but highly diverse group of GEP malignancies [1, 2, 7]. Those neoplasms originate from neuroendocrine-type cells throughout the GEP system, with more than 50% located in the pancreas [5, 14, 15]. This is related to a high concentration of cell progenitors in the pancreatic islets. Only 5%–25% of NETs occur in the setting of genetic predisposition. Those include multiple endocrine neoplasia (MEN)-1, MEN-2, neurocutaneous syndromes (von Recklinghausen disease, von Hippel–Lindau syndrome, tuberous sclerosis, and Sturge–Weber syndrome), with the majority of NETs occurring sporadically [6, 8, 15]. Historically, due to NET heterogeneity, it has been difficult to obtain worldwide consensus on their classification; however, in 2000 the World Health Organization adopted the classification based on histologic grade that facilitated consistent nomenclature [1, 17]. Further, the North American Neuroendocrine Tumor Society and European Neuroendocrine Tumor Society have developed guidelines and recommendations that were incorporated in the 2009 tumor–node–metastasis (TNM) classification of the Union for International Cancer Control, as well as in WHO 2010 [2].
