Neuroendocrine Tumors of the GI Tract: Patient Education

Cancer Facts

According to the American Cancer Society:

  • There are around 11,000 to 12,000 neuroendocrine tumors and neuroendocrine cancers diagnosed each year in the United States. About 2 out of 3 of these occur in the digestive system. Most of the rest occur in the lungs, although a small number develop in other organs.
  • The number of carcinoid tumors diagnosed has been increasing for many years. The reason for this is unknown. Some think it may be a byproduct of doing more endoscopy and CT scans to look for something else and finding carcinoid tumors.
  • Since many carcinoids never cause any symptoms, there are probably many people with carcinoid tumors that are never found. These tumors may be discovered during an autopsy when a person dies of something else, or when a person has surgery or imaging tests for an unrelated condition.
  • Carcinoids are more common in African Americans than in whites, and are slightly more common in women than men.


According to the American Society of Clinical Oncology:

  • Islet cell tumors are uncommon, with 200 to 1,000 cases diagnosed each year in the United States.
  • Islet cell tumors are often treatable.


Neuroendocrine tumors of the gastrointestinal (GI) tract are abnormal growths that begin in your body’s digestive system.

They may be noncancerous (benign) or cancerous (malignant).

Your GI tract contains neuroendocrine cells that secrete hormones in response to certain stimuli during the digestive process. Because they produce hormones, they are part of your endocrine system. Consequently, their treatment requires the expertise and skill of endocrine specialists.

How Neuroendocrine Tumors of the GI Tract Grow

As with other tumors, the neuroendocrine cells in your GI tract in some cases alter and grow too many cells, forming tumors called neuroendocrine tumors (NETs).

As neuroendocrine tumors grow, they release hormones into your GI tract. This overproduction of hormones can cause signs and symptoms related to the specific hormone that is overproduced.

If the tumor is malignant and left untreated, cancer can spread through your lymph system and bloodstream to other organs in your body.

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Types of Neuroendocrine Tumors of the GI Tract

Carcinoid Tumors of the GI Tract

  • Located in the stomach, intestine, appendix or rectum
  • Always malignant
  • Usually slow growing

Islet Cell Tumors of the Pancreas

  • Located in the islet cells of the pancreas (also known as the islets of Langerhans)
  • May be benign or malignant

There are six subtypes of islet cell tumors of the pancreas.


  • Located in the pancreas or small intestine
  • Overproduction of gastrin can cause too much stomach acid in a condition called Zollinger-Ellison syndrome
  • About half are malignant
  • May spread to liver and nearby lymph nodes


  • Located in the pancreas
  • Overproduction of insulin can cause low blood sugar (hypoglycemia)
  • Most insulinomas are benign


  • Located in the islet cells of the pancreas
  • Overproduction of glucagon can cause high blood sugar (hyperglycemia)
  • Usually cancerous (malignant)


  • Located in the head of the pancreas
  • Overproduction of somatostatin halts the production of other hormones (gastrin, growth, insulin)


  • Located in the islet cells of the pancreas
  • Overproduction of hormone vasoactive intestinal peptide (VIP) causes hypokalemia and achlorhydria (low stomach acid)

Non-functional Islet Cell Tumors of the Pancreas (Ppoma)

  • Though these tumors are located in the islet cells of the pancreas, they don’t overproduce the hormones described above.
  • Consequently, they often don’t cause symptoms, or their symptoms are not easily identifiable.
  • As a result, they are often diagnosed at later stages of disease.

Islet cell tumors of the pancreas are also called:

  • Pancreatic islet cell tumors
  • Pancreatic endocrine tumors
  • Islet of Langerhans tumors
  • Neuroendocrine tumors

If the pancreatic endocrine tumor produces hormones, it’s called a functioning tumor. If it doesn’t make hormones, it’s considered a nonfunctioning tumor.

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Related Resources

Carcinoid Tumors of the GI Tract

Islet Cell Tumors of the Pancreas

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