Neuroendocrine Tumors: Where and Why They Develop

What are neuroendocrine tumors?

Neuroendocrine tumors develop in neuroendocrine cells. These cells are found in almost every organ of your body. Their function is to release hormones in response to signals from your nerves. For example, neuroendocrine cells in your adrenal glands release the hormone epinephrine (adrenaline) in response to stress.

Previously, neuroendocrine tumors were classified as cancerous or noncancerous, but now all neuroendocrine tumors are considered cancer.

Neuroendocrine tumors can either be classified as functioning or nonfunctioning:

• Functioning tumors produce excess hormones that cause symptoms.
• Nonfunctioning tumors don’t produce excess hormones or not enough to cause symptoms.

The number of neuroendocrine tumors diagnosed each year in the United States is steadily increasing, likely due to better detection.

Where do neuroendocrine tumors typically develop? 

Neuroendocrine tumors can develop in almost any organ but are most common in your digestive tract.

• about 12 to 27 percent occur in the rectum
• about 20 percent occur in the large intestine
• about 19 percent occur in the small intestines
• about 4 percent occur in the appendix

The next most common place for these tumors to develop is your lungs. About 30 percent of endocrine tumors develop in your lungs. About 7 percent develop in the pancreas.

Roughly 15 percent of neuroendocrine tumors are found outside the gastrointestinal tract, pancreas, or lungs.

What are the signs and symptoms of a neuroendocrine tumor?

The signs and symptoms of neuroendocrine tumors vary widely based on where the tumor develops. Other factors that determine symptoms include:

• tumor size
• the type of tumor
• whether the cancer produces hormones
• whether it has metastasized (spread to distant parts of your body)

Often, people with neuroendocrine tumors don’t have any symptoms until the tumor grows large enough to impair organ function.

Symptoms can be broadly categorized as:

• hormonal: Excess hormones produced by the tumor can cause symptoms such as poor blood sugar control, diarrhea, or gastric ulcers, depending on where the tumor forms.
• mechanical: The tumor can cause symptoms by putting physical pressure on an organ. For example, a tumor in your intestines may cause bowel obstruction.

Symptoms of gastrointestinal tumors

Here are some of the typical symptoms of tumors affecting the gastrointestinal system or pancreas:

Symptoms of lung tumors

Here are the main symptoms for lung neuroendocrine tumors:

What causes a neuroendocrine tumor to form and who’s at risk?

Researchers aren’t entirely sure why some people develop neuroendocrine tumors. Most of these tumors occur in people with no family history.

Some genetic cancer syndromes increase your risk. These include:

• multiple endocrine neoplasia type 1
• Von Hippel-Lindau disease
• tuberous sclerosis
• neurofibromatosis type 1

All these conditions are autosomal dominant, meaning they develop if you get the gene from one parent.

Other risk factors include:

• race: White people have a higher risk than Black people of developing neuroendocrine tumors overall, but the risk varies between specific types.
• gender: Women develop neuroendocrine tumors slightly more often than men.
• age: Neuroendocrine tumors are rare in childhood.
• certain medical conditions: Some medical conditions may put you at an increased risk of developing certain types of neuroendocrine tumors. For example, reduced stomach acid production increases the risk of neuroendocrine tumors in the stomach.

How are neuroendocrine tumors diagnosed?

Diagnosing neuroendocrine tumors can be difficult because symptoms are often nonspecific. A nonspecific symptom is something that a person feels or reports but can’t be observed by a doctor. Examples include chronic fatigue or pain unrelated to an injury.

Neuroendocrine tumors may be found incidentally while testing for other conditions. One survey of 1,928 people found an average delay of 52 months between symptom onset and diagnosis.

To confirm diagnosis, doctors may use a number of different tests, including:

• blood tests
• urine tests
• imaging
• biopsy, a small tissue sample

Imaging tests may include:

• ultrasound
• computerized tomography (CT) scan
• magnetic resonance imaging (MRI)
• positron emission tomography (PET) scan
• octreotide scan, where a special camera looks at a radioactive dye in your blood

How are neuroendocrine tumors treated?

Treatment for neuroendocrine tumors depends on factors such as:

• tumor location
• aggressiveness
• how advanced the cancer is
• your overall health
• whether the tumor is producing excess hormones

Neuroendocrine tumors usually grow slowly when they’re in your gastrointestinal tract or appendix.

Active surveillance

If the tumor is slow-growing, your doctor may recommend active surveillance. With active surveillance, your tumor is monitored regularly but you’re not given specific treatment.

Surgery with or without chemotherapy or radiation therapy

If the tumor hasn’t spread beyond the organ of origin, it may be removed surgically. Chemotherapy or radiation therapy may be used to shrink tumors either with surgery or by themselves.

A form of internal radiation therapy called peptide receptor radionuclide therapy was FDA-approved in 2018 to treat advanced gastrointestinal and pancreatic neuroendocrine tumors.

Medications

Your doctor may recommend medications called somatostatin analogs such as octreotide or lanreotide.

These medications prevent your body from producing too many hormones and may improve symptoms. They’re generally administered as an injection every 28 days.

What’s the outlook for neuroendocrine tumors?

The American Cancer Society uses information from the SEER database to track 5-year relative survival rates for neuroendocrine tumors. A relative survival rate compares people with the same type and stage of tumors to people without tumors in the overall population.

The 5-year relative survival rates listed in the table below are estimates based on previous outcomes. They don’t take into account your age, overall health, and how well your cancer is responding to treatment. Keep in mind that cancer treatments also improve over time, so people being diagnosed today may have better outlooks.

It’s always best to discuss your specific outlook with your doctor or oncology team. They know more about your particular situation, and can give you a more accurate, personalized understanding of these numbers.

5-year relative survival rates for neuroendocrine tumors

Takeaway

Neuroendocrine tumors can develop in almost any organ in your body, but they most commonly form in your digestive tract, lungs, or pancreas.

Symptoms can vary widely depending on where the tumor forms. They can lead to hormone problems if the tumor produces excess hormones.

It’s critical to visit your doctor as soon as possible if you suspect you may have a neuroendocrine tumor or any other type of cancer. Cancer treatment is most effective when it’s begun in the early stages.