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Neuroendocrine tumors, or more properly gastro-entero-pancreatic or gastroenteropancreatic neuroendocrine tumors (GEP-NETs), are cancers of the interface between the endocrine (hormonal) system and the nervous system.
The endocrine system is a communication system in which hormones act as biochemical messengers to regulate physiological events in living organisms. The nervous system performs the same functions using electrical impulses as messengers. The neuroendocrine system is the combination of those two systems, or more specifically, the various interfaces between the two systems. A GEP-NET is a tumor of any such interface.
More specifically, the endocrine system is primarily a network of glands that produce and secrete hormones, usually into the bloodstream. It also includes cells that are not part of glands: the diffuse neuroendocrine system, scattered throughout other organs.
A hormone is a chemical that delivers a particular message to a particular organ, typically remote from the hormone’s origin. For example, the hormone insulin, secreted by the pancreas, acts primarily to allow glucose to enter the body’s cells for use as fuel. The hormone gastrin is secreted by the stomach to tell the stomach to produce acids to digest food.
Hormones can be divided into subtypes such as peptides, steroids, and neuroamines. For some researchers, there is no clear distinction between peptide hormones and peptides; the hormones are simply longer than other peptides. In the context of GEP-NETs, the terms hormone and peptide are often used interchangeably.
The vast majority of GEP-NETs fall into two nearly distinct categories: carcinoids, and pancreatic endocrine tumors (PETs). Despite great behavioral differences between the two, they are grouped together as GEP-NETs because of similarities in cell structure. [1]
Siegfried Oberndorfer, in 1907, was the first person to distinguish clearly what we now call GEP-NETs from other forms of cancer. He gave the term “carcinoid” to these tumors, because they were so slow-growing that he considered them to be “cancer-like” rather than truly cancerous. In 1929, he reported that some such tumors were not so indolent – these he distinguished as what we now call PETs from what most authorities call carcinoids. Despite the differences between the two categories, some doctors, including oncologists, persist in calling all GEP-NETs “carcinoid”, even into the twenty-first century. [2]
Pancreatic endocrine tumors (PETs) are also known as endocrine pancreatic tumors (EPTs) or islet cell tumors. PETs are assumed to originate generally in the islets of Langerhans within the pancreas – or, Arnold et alia suggest, from endocrine pancreatic precursor cells (Arnold et al. 2004, 199) – though they may originate outside of the pancreas. (The term pancreatic cancer almost always refers to adenopancreatic cancer, also known as exocrine pancreatic cancer. Adenopancreatic cancers are generally very aggressive, and are not neuroendocrine cancers. About 95 percent of pancreatic tumors are adenopancreatic; about 1 or 2 percent are GEP-NETs.) [3]
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