NENs are a type of cancer that starts in the neuroendocrine cells. These specialized cells are nerve cells that produce hormones like endocrine cells. NENs can occur anywhere in the body.

Anyone can develop NENs, but they are more common in some people than others:

• Adults are more likely to develop NENs than children.
• NENs are slightly more common in women than men, although it’s not clear why.
• NENs are more common in white people than Black people, although the location of a NEN varies by race.

Certain medical conditions can also increase the risk of developing NENs. These include:

• Multiple endocrine neoplasia, type 1 (MEN 1) and type 2 (MEN 2) — A group of disorders that affect the endocrine system. The different types affect different genes and hormones, and have different signs and symptoms.
• Neurofibromatosis — A group of genetic disorders that cause tumors to form on nerve tissue.
• Tuberous sclerosis — A genetic disorder caused by gene changes that cause non-cancerous tumors to grow in the brain and other parts of the body.
• Von Hippel-Lindau disease — An inherited, multi-system disorder that causes non-cancerous tumors to grow in certain parts of the body.

Experts do not know what causes NENs to form. However, patients with multiple endocrine neoplasia with changes in the MEN1 gene have a higher chance of developing carcinoid tumors. The MEN1 gene may play a role in the development of NENs in the lungs and digestive tract.

The signs and symptoms of a NEN depend on where the tumor is located, and whether it is functional or non-functional. Functional NENs produce excess hormones and cause symptoms, while non-functional NENs do not produce hormones or produce very little hormones.

Common NENs symptoms include:

• Fatigue and weakness
• Nausea or vomiting
• Pain from a growing tumor
• Unexplained weight loss

Other symptoms that can occur with functional NENs include:

• Diarrhea
• Dizziness or shakiness
• Frequent urination
• Increased thirst
• Skin rash or flushing

Diagnosing a NEN depends on where it is located in your body. Generally, diagnostic tests include:

• Physical exam to look for swollen lymph nodes or other signs of excess hormone production.
• Imaging tests such as CT, MRI, or ultrasound to take pictures of the tumor.
• Biopsy to remove a sample of the tumor cells.
• Blood or urine test to look for signs of excess hormone production.

Treatment options for NENs depend on the type of tumor, its location, and whether you are experiencing symptoms.

Treatment options include:

• Surgery. Surgery removes the tumor as well as some of the healthy surrounding tissue. If the surgeon cannot remove the tumor completely, they will remove as much of it as possible. Surgery is the best option for treating carcinoid tumors.
• Chemotherapy. Chemotherapy uses strong drugs to kill the tumor cells. Chemotherapy is usually recommended for advanced tumors that cannot be removed with surgery. It can be used alone or in combination with other treatments.
• Targeted drug therapy. Targeted drug therapy uses drugs that target abnormalities within cancer tumor cells. Targeted drug therapy is often combined with chemotherapy for advanced tumors.
• Peptide receptor radionuclide therapy. Peptide receptor radionuclide therapy uses high doses of radiation to destroy or slow the growth of tumors and reduce the side effects of the disease.
• Radiation therapy. Radiation therapy uses high-energy X-rays to destroy tumor cells. External-beam radiation therapy is the most common type of radiation treatment for NENs.
• Medication. Medication is used to destroy cancer cells. A patient may take medication intravenously (through the vein using a needle) or in a pill or capsule form. They may also receive an injection into the muscle.

NENs do not appear to be hereditary, meaning they don’t run in families. However, some people may have a genetic risk. People who have multiple endocrine neoplasia have a higher risk of getting carcinoid tumors.

A prognosis is a doctor’s best estimate of how a disease will affect you and how it will respond to treatment. The prognosis for a NEN depends on several different factors. NENs caught in the early stages before they have had a chance to spread to other parts of the body are easier to treat and have favorable prognoses. NENs that are caught in the later stages and have spread have a less favorable prognosis.

Other factors that can affect the prognosis and survival rate for a NEN include:

• Grade and differentiation
• Hormone production (functional vs. non-functional)
• Location
• Size