The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on September 21, 2021.

About neuroendocrine tumors (NETS)

A neuroendocrine tumor (NET) begins in the specialized cells of the body’s neuroendocrine system. These cells have traits of both hormone-producing endocrine cells and nerve cells. They are found throughout the body’s organs and help control many of the body’s functions. Hormones are chemical substances that are carried through the bloodstream and have a specific effect on the activity of other organs or cells in the body. All NETs are considered malignant tumors. Most NETs take years to develop and grow slowly. However, some NETs may be fast-growing.

NETs comprise a small fraction of new cancer cases, accounting for more than 12,000 new diagnoses each year. But incidence rates have been rising over the past 15 years.

What causes neuroendocrine tumors (NETS)?

There is no one cause or specific risk factors associated with NETs. There are, however, factors that may raise a person’s risk for developing a NET, including:

Inherited syndromes: Multiple endocrine neoplasia type 1 (MEN1) is a hereditary condition associated with certain types of NETs, including lung NETs, GI tract NETs, and pancreatic NETs. Other hereditary conditions related to NETs include Von Hippel-Lindau syndrome, neurofibromatosis type 1, multiple endocrine neoplasia type 2 (MEN2), and tuberous sclerosis complex.

Other medical conditions: Certain diseases can put people at greater risk of developing specific types of NETs. For example, people with diseases that damage the stomach and reduce acid production have a greater risk of developing a NET of the stomach.

Environment and diet: Based on known data, there is no connection between NETs and the environment or diet.

Who gets neuroendocrine tumors (NETs)?

Statistically, whites are more likely to develop a NET than other ethnic groups. Also, for unknown reasons, NETs are slightly more common in women than in men.

Neuroendocrine tumor (NET) types

NETs can begin in any part of the body, including the:

  • Lungs
  • Gastrointestinal tract (stomach, pancreas, appendix, intestines, colon and rectum)
  • Thyroid gland
  • Adrenal gland
  • Pituitary gland

Doctors may classify a NET tumor by its site of origin, such as GI NET, pancreatic NET or lung NET. NET tumors are almost always considered to be malignant or cancerous.

Learn more about types of neuroendocrine tumors

Neuroendocrine tumor (NET) symptoms and signs

Symptoms associated with a NET tumor depend on the location of the tumor, and whether the NET is found to be functional or nonfunctional. Functional NETs are categorized by the presence of clinical symptoms due to excess hormone secretion by the tumor. Nonfunctional NETs do not secrete hormones. They may produce symptoms caused by the tumor's growth.

Common symptoms of NETs include:

  • Flushing (redness, warmth) in the face or neck without sweating
  • Persistent pain in a specific area of the body
  • Diarrhea, including at nighttime
  • Thickening or a lump in any part of the body
  • Nausea or vomiting
  • Changes in bowel or bladder habits
  • Shortness of breath, rapid heartbeat/palpitations
  • High blood pressure
  • Fatigue and weakness
  • Abdominal pain, cramping, feeling of fullness
  • Unexplained weight gain or loss
  • Wheezing, coughing or hoarseness that doesn't go away
  • Swelling in the feet and ankles
  • Skin lesions, discolored patches of skin, thin skin, skin rash
  • High blood glucose levels (frequent urination, increased thirst, increased hunger)
  • Low blood glucose levels (shakiness, dizziness, sweating, fainting)
  • Jaundice
  • Unusual bleeding or discharge
  • Anxiety
  • Confusion
  • Nutritional deficiencies

Like many cancers, the symptoms of NET tumors can be similar to those caused by other, non-cancerous conditions, which may lead to a misdiagnosis or a delayed diagnosis. That’s why many NETs are diagnosed at an advanced stage.

Learn more about symptoms of neuroendocrine tumors

Neuroendocrine tumor (NET) stages

Staging is a way of describing where the tumor is located, if or where it has spread, and whether it is affecting other parts of the body. Staging a NET tumor is key in developing the appropriate treatment plan. Diagnostic testing is used by doctors to determine the stage of a NET tumor and to better predict a patient’s prognosis. There are different stage descriptions for different types of NETs.

NETs may:

  • Be contained in a particular area of the body (localized)
  • Have spread to nearby tissues or lymph nodes (regional)
  • Have spread throughout the body (metastatic)

The World Health Organization (WHO) classifies neuroendocrine tumors according to the malignant potential of the tumor:

  • Well-differentiated neuroendocrine tumors (grade 1 and 2)
  • Poorly differentiated neuroendocrine tumors (grade 3)

NETs of the GI tract and pancreas have their own staging systems based on the location and characteristics of the tumor. Some NETs use the staging system for other cancers. For example, the staging of a lung NET is the same as the staging of non-small cell lung cancer. These staging systems are created by the American Joint Committee on Cancer (AJCC).

Learn more about stages of neuroendocrine tumors

Diagnosing neuroendocrine tumors (NETs)

Most NETs are found unexpectedly when people undergo testing for reasons unrelated to the tumor. Since NET tumors can found in many locations in the body, diagnosing them requires a unique approach depending on the type of tumor, its location, whether it produces excess hormones, how aggressive it is and whether it has spread to other parts of the body.

At CTCA®, our cancer experts use a variety of tools and techniques for diagnosing neuroendocrine tumors, evaluating the disease and planning each patient’s individualized treatment. The diagnostic tests that may be used to diagnose NETs include:

  • Lab tests, cytopathology
  • Biopsy, endoscopic ultrasound
  • Endoscopic retrograde cholangiopancreatography (ERCP)
  • Computerized tomography scan (CT scan)
  • Computerized tomography (CT) angiography
  • Magnetic resonance imaging (MRI)
  • Laparoscopy
  • Nuclear medicine imaging
  • Genetic testing and counseling

Learn about diagnostic procedures for neuroendocrine tumors

Treating neuroendocrine tumors (NETs)

Treatment options for NETs include:

  • Surgery: Minimally invasive procedures using laparoscopy or laparotomy, either to remove the entire tumor or to reduce its mass if it cannot be completely removed, may be recommended. Mesenteric resections for small bowel tumors and cytoreductive surgery may be recommended for advanced-stage disease.
  • Immunotherapy: These treatments use the drug interferon, which helps stimulate the immune system.
  • Targeted therapy: These drugs attack certain areas of the cancer cell or its environment (including genes and proteins) that may be responsible for the tumor’s growth.
  • Chemotherapy: These drugs are designed to interfere with the growth of cancer cells in order to destroy them.
  • Interventional radiology: This field of medicine uses both catheter- and needle-based therapies.

Peptide receptor radionuclide therapy: PRRT combines a cell-targeting protein (or peptide) with a radionuclide (or radioactive material), given intravenously to deliver a high dose of radiation to the tumors.

Learn about treatment options for neuroendocrine tumors