Neuroendocrine gastroenteropancreatic tumors (GEP-NETs) constitute a heterogeneous group of tumors with their origin in neuroendocrine cells of the embryological gut. Most commonly, the primary lesion is located in the gastric mucosa, the small and large intestine, the rectum and pancreas. The crude incidence has significantly increased over the last years and is now estimated to be 5.25/100 000/year. The prevalence has recently been calculated to 35/100 000/year. The incidence for small intestinal neuroendocrine tumor (NETs) (carcinoids) is estimated to be from 0.32/100 000/year (England) to 1.12/100 000/year (Sweden). The incidence for rectal tumors is 0.86/100 000/year, for pancreatic 0.32/100 000/year and for gastric NETs 0.30/100 000/year. Neuroendocrine GEP tumors can appear at all ages, with the highest incidence being from the fifth decade onward. The exception is the carcinoid of the appendix, which occurs with the highest incidence at ～40 years of age. There is a slight overall higher incidence of NETs for males (5.35) compared with females (4.76). Patients with multiple endocrine neoplasia type 1 (MEN-1) or von Hippel–Lindau’s disease (VHL), may have a clinical onset 15–20 years earlier than patients with corresponding sporadic type of neuroendocrine tumors .
