Pancreatic neuroendocrine tumors (pancreatic NETs or PNETs) account for less than 10% of all pancreatic tumors. They may be benign or malignant and they tend to grow slower than exocrine tumors. They develop from the abnormal growth of endocrine (hormone-producing) cells in the pancreas called islet cells. This is why these tumors are sometimes referred to as “islet cell tumors.”

Some of the hormones islet cells produce include insulin, glucagon and somatostatin. Insulin and glucagon are the two main pancreatic hormones. Insulin lowers blood sugar levels, while glucagon raises blood sugar levels. Together, these two main hormones work to maintain the proper level of sugar in the blood. Somatostatin regulates the levels of a variety of other hormones in the blood.

Pancreatic neuroendocrine tumors are either functional (produce hormones) or nonfunctional (produce no hormones).

Functional neuroendocrine tumors cause the pancreas to overproduce hormones consequently causing hormone-related symptoms. The majority of PNETs are nonfunctional tumors. Nonfunctional tumors do not produce any hormones so they do not cause any hormone-related symptoms. As a result, these tumors are typically diagnosed once the tumor is advanced and is causing symptoms such as pain or jaundice.

The following are the different types of pancreatic neuroendocrine tumors classified by the hormones that they produce.

Gastrinoma (Zollinger-Ellison Syndrome)
Gastrinomas produce gastrin. When this tumor is inherited as part of a genetic syndrome called Multiple Endocrine Neoplasia Type 1 (MEN1) (see below), multiple tumors may be found in the head of the pancreas and/or the duodenum. They have a very high potential to become malignant.

Glucagonoma
Glucagonomas produce glucagon. They are commonly found in the body and tail of the pancreas. They are usually large, often metastasize and have a very high potential to become malignant.

Insulinoma
Insulinomas produce insulin. They are the most common type of functional pancreatic neuroendocrine tumor. They tend to be small and hard to diagnose. Most of them are benign.

Somatostatinoma
Somatostatinomas produce somatostatin. They are extremely rare and usually very large. They can occur anywhere in the pancreas and in the duodenum. They have a very high potential to become malignant.

VIPoma (Verner-Morrison Syndrome)
VIPomas produce vasoactive intestinal peptide (VIP). Two-thirds of VIPomas are found in women. The syndrome is also known as Watery Diarrhea and Hypokalemia Achlorhydria (WDHA) Syndrome. They have a high potential to become malignant.

Nonfunctional Islet Cell Tumor
Nonfunctional islet cell tumors are usually malignant. They are hard to detect.

Multiple Endocrine Neoplasia Type-1 (MEN1)
MEN1 (also known as Wermer Syndrome) is a hereditary syndrome that causes multiple tumors in the parathyroid and pituitary glands, and the pancreas. It is suspected when tumors are found in at least two of the three endocrine glands mentioned above. About 30-75% of people with MEN1 will develop pancreatic neuroendocrine tumors. Gastrinomas are the most common pancreatic neuroendocrine tumors in individuals with MEN1. The second most common are insulinomas. The tumors in the pancreas may be malignant and generally appear in individuals in their 30’s or 40’s.

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