What Are Neuroendocrine Tumors? Causes, Symptoms, and Treatments to Know

Neuroendocrine tumors (NETs) are a rare type of tumor. Only about 12,000 people in the U.S. are diagnosed with NETs per year. There are many different types of NETs, and they can occur anywhere in the body. These tumors equally affect men and women. But they grow slowly and are very treatable.

In this article, we discuss the details of NETs, from causes and symptoms to diagnosis and treatment. 

What are neuroendocrine cells?

To understand NETs, you first need to understand a bit about the cells they come from: neuroendocrine cells. “Neuro” means nerves, and “endocrine” means hormones. So neuroendocrine cells are special cells that respond to signals from nerves by releasing hormones. 

Neuroendocrine cells are found all over the body, such as in the:

• Stomach and bowels (gastrointestinal, or GI, tract)

• Lungs

• Pancreas

• Pituitary gland (brain)

• Adrenal glands 

• Thyroid and parathyroid glands in the neck

• Kidneys and bladder

• Genital organs (like the ovaries and prostate)

• Skin

What causes neuroendocrine tumors?

NETs happen when a neuroendocrine cell becomes cancerous. Cancerous cells result from changes (mutations) in DNA that cause them to reproduce rapidly. The more copies a cancerous cell makes of itself, the bigger the tumor. 

Some NETs are hereditary — meaning they’re related to genetic conditions that cause tumors. An example of a hereditary NET is multiple endocrine neoplasia type 1 (MEN1). But most NETs are sporadic — meaning they happen out of nowhere.

How are neuroendocrine tumors different from other tumors?

NETs differ from other tumors in two ways:

1. Location: Neuroendocrine cells exist all over the body, and so do NETs. This makes them different from other tumors, which start in specific organs. For example, breast cancer starts in the breast. But NETs can start anywhere. The most common locations include the GI tract (65% of cases) and lungs (25%).

2. Release of hormones: Some NETs are “functional” — meaning they release more hormones than they should. This excess of hormones leads to NETs having specific symptoms that other tumors don’t have (more on this below). 

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What are the different types of NETs?

Neuroendocrine tumors can start in many different parts of the body. Here are some of the most common types:

• NETs of the GI tract, lungs, or pancreas 

• Pheochromocytomas (typically found in the adrenal gland)

• Paragangliomas (in the head, neck or torso)

• Pituitary NET

• Medullary thyroid cancer

• NETs of the reproductive system

• Merkel cell carcinoma (develops in areas of skin highly exposed to the sun)

What are the symptoms of a neuroendocrine tumor?

Since there are so many different kinds of neuroendocrine tumors, symptoms vary. Every person has their own unique combination of symptoms, and some people may not have symptoms at all. 

Symptoms fall into three main categories.

1. General cancer symptoms

The symptoms of an NET are similar to those of general cancer, such as:

• Weight loss

• Lack of appetite

• Fatigue

2. Symptoms related to tumor location

Other symptoms can depend on where the NET is located, such as:

• Pain in the affected location

• A red, brown, or purple lump or growth on the skin

• Shortness of breath, cough, or coughing up blood (tumors in the lung)

• Diarrhea, constipation, or bloody stools (tumors in the GI tract)

3. Symptoms related to the release of hormones

As we said above, NETs have different symptoms than other tumors due to the excess hormones that they release. Here are some of these symptoms:

• Abdominal pain, stomach ulcers, and diarrhea — when NETs release too much stomach acid 

• Low blood sugar — when NETs release too much insulin

• Flushing of the face, wheezing, rapid heartbeat, and diarrhea (carcinoid syndrome)

How do you diagnose a neuroendocrine tumor?

NETs can be harder to diagnose than other types of tumors since there are so many different kinds of them. NETs that release hormones tend to be diagnosed earlier. That’s because the symptoms of too much hormone prompt people to seek medical care sooner. 

To diagnose a NET, a healthcare professional might order any of these tests:

• CT or MRI imaging

• Endoscopy, which involves inserting a camera into the stomach or rectum to examine the inside of the stomach or bowels

• Special imaging, which involves injecting a radioactive substance into a vein to locate tumor cells (like octreotide scans)

• Blood or urine tests to check hormone levels (tumor markers)

NETs can be diagnosed by a primary care provider or in the emergency room (ER). Once testing confirms a cancer diagnosis, an oncologist (cancer specialist) will take the lead when it comes to treatment.

How do you treat a neuroendocrine tumor?

Most neuroendocrine tumors are very treatable. Treatment depends on a couple of different factors, like:

• Type of neuroendocrine cell causing the NET and whether it makes hormones

• Location of the NET

• Any metastasis (spread) of the NET and how quickly the NET is growing or spreading

Here are some of the treatment options that can be used to treat NETs: 

• Surgery to remove the tumor if it hasn’t spread yet

• Chemotherapy medications

• Targeted therapy (medications that target specific parts of cancer cells)

• Medications to manage symptoms (like diarrhea)

Keep in mind, some people may need a combination of different therapies. And it’s important to note that a solid support system and tools to help cope with a cancer diagnosis and treatment are really important too.

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Written by:

Samantha C. Shapiro, MD

Samantha Shapiro, MD, is a board-certified rheumatologist and internist with expertise in autoimmune and inflammatory conditions. She founded the division of rheumatology at Dell Medical School at The University of Texas at Austin.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Maria Robinson, MD, MBA

Maria Robinson, MD, MBA, is a board-certified dermatologist and dermatopathologist who has practiced dermatology and dermatopathology for over 10 years across private practice, academic, and telehealth settings. She is a fellow of the American Academy of Dermatology and the American Society of Dermatopathology.

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