What Is the Most Common Pancreatic Neuroendocrine Tumor? Insulinomas

What is a pancreatic neuroendocrine tumor?

Two main types of tumors form in the pancreas.

Pancreatic exocrine tumor

Exocrine tumors begin in the cells of the pancreas that secrete enzymes, which help digests food.

Pancreatic neuroendocrine tumor

A pancreatic neuroendocrine tumor is developed from the abnormal growth of endocrine cells (also called islet cells), the cells that are involved in the secretion of hormones. It is also called an islet cell tumor, which forms about seven percent of all pancreatic tumors. These tumors may be noncancerous (benign) or cancerous (malignant), and their growth is slower than pancreatic exocrine tumors.

The hormones produced by the islet cells include:

• Insulin: Lowers blood sugar levels
• Glucagon: Raises blood sugar levels
• Somatostatin: Regulates the blood levels of other hormones

Pancreatic neuroendocrine tumors can be either functional or nonfunctional.

Functional pancreatic neuroendocrine tumors secrete abnormal levels of hormones, so the presented symptoms are typically hormone-related.

Nonfunctional tumors do not secrete hormones and do not produce symptoms unless they are big or spread to other parts of the body.

How is an insulinoma diagnosed?

The doctor will order blood tests that look for the levels of various hormones secreted by the pancreas. An increased insulin level with a low blood sugar level indicates insulinoma.

Other tests used for the diagnosis of insulinoma include:

• Seventy-two hours fast: The patient will be asked to stay in the hospital and fast for 72 hours for this test. The blood sugar level will be monitored every six hours. If the patient has insulinoma, they will develop a very low blood sugar level within 48 hours.
• Magnetic resonance imaging (MRI) or computed tomography (CT) scan: MRI or CT scan will provide detailed images of the pancreas and help the doctor confirm their diagnosis, know the size and location of the tumor.
• Endoscopic ultrasound (EUS): EUS may be used if the tumor is not detected by a CT or MRI scan. This test uses a thin tube fitted with an ultrasound probe that is inserted through the mouth or nose so that it gets very close to the pancreas. If an abnormal growth is seen, a biopsy needle can be passed down the endoscope to get samples of the abnormal tissue.

What are the other types of pancreatic neuroendocrine tumors?

Other neuroendocrine tumors are less common than insulinoma and include:

• Gastrinoma (Zollinger–Ellison syndrome): Gastrinomas produce gastrin, which produces stomach acid. These have a high potential to become cancerous. For people who have the syndrome called multiple endocrine neoplasia type I, multiple tumors may develop in the head of the pancreas and duodenum.
• Glucagonoma: Glucagonomas produce glucagon, which controls blood sugar levels. These have a high potential to develop into cancer. Commonly found in the body and tail of the pancreas, these are usually large tumors that can spread to other organs.
• Somatostatinoma: Extremely rare and large tumors, somatostatinomas produce somatostatin. They can form anywhere in the pancreas and duodenum and tend to become cancerous.
• VIPoma (Verner–Morrison syndrome): VIPomas produce vasoactive intestinal peptides. Women are more likely to develop this kind of tumor than men. They have a high potential to turn cancerous.
• Nonfunctional islet cell tumor: Nonfunctional islet cell tumors are hard to detect and are usually cancer-forming.