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Pancreatic Neuroendocrine Tumors

The pancreas is a gland that produces hormones, such as insulin (which helps control blood sugar levels) and digestive juices. 

Pancreatic neuroendocrine tumors (NETs), formerly called islet cell tumors, are rare cancers that arise from hormone-producing cells in the pancreas. Only about 2,500 cases of pancreatic neuroendocrine tumors are reported in the U.S. each year. Pancreatic NETs make up only about 2% of all pancreatic tumors.

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Causes of Pancreatic NETs

Pancreatic neuroendocrine tumors grow from islet cells in the pancreas. Normal islet cells produce hormones such as insulin and glucagon. Many islet cell tumors also produce pancreatic hormones, which leads to an excess of these hormones in the body.

Many different cells in the body can turn cancerous, including cells of the pancreas. People with a family history of an endocrine disorder called multiple endocrine neoplasia type 1 (MEN1) are at greater risk for pancreatic NETs. The risk also increases in people who have von Hippel-Lindau disease, neurofibromatosis type 1, or tuberous sclerosis.

Types of Pancreatic NETs

Pancreatic neuroendocrine tumors can be noncancerous or cancerous.

Two main types of pancreatic NETs exist:

Nonfunctional NETs make up about half of all pancreatic NETs. These tumors release hormones that don't cause symptoms. Most nonfunctional tumors are cancerous. 

Functional pancreatic NETs release hormones into the bloodstream that cause symptoms. These tumors are often noncancerous. Their names are based on the hormone they produce:

Insulinomas. These are the most common functioning tumors of the pancreas. They form in the cells that produce insulin, a hormone that helps the body regulate glucose (blood sugar). The excess insulin produced by these tumors can lead to low blood sugar. Insulinomas are rarely cancerous.

Gastrinoma. These tumors occur in patients with a rare disorder called Zollinger-Ellison syndrome. Gastrinomas form in the cells that produce the hormone gastrin, which triggers the stomach to release acid. A gastrinoma can lead to increased stomach acid production. Most gastrinomas are cancerous.

Glucagonoma. This tumor forms in the cells that produce glucagon, a hormone that increases the blood sugar level. Glucagonomas can lead to high blood sugar levels. Most glucagonomas are cancerous.

VIPoma. VIPomas form in the cells that produce vasoactive intestinal peptide (VIP), a hormone that aids in gastrointestinal movement. This type of NET is very rare, but about half of all cases that do occur are cancerous.

Somatostatinoma. This tumor grows in the cells that produce somatostatin, a hormone that helps control the production of other hormones, including insulin and gastrin. More than two-thirds of these tumors are cancerous. 

In rare cases, pancreatic NETs can also release other types of hormones.

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