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Symptoms of neuroendocrine tumors

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.

Different types of neuroendocrine tumors (NET) cause different symptoms, depending on the location of the tumor, and whether the NET is functional or nonfunctional. Functioning NETs are defined based on 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
  • Diarrhea, including at nighttime
  • Shortness of breath, rapid heartbeat/palpitations
  • High blood pressure
  • Fatigue, weakness
  • Abdominal pain, cramping, feeling of fullness
  • Unexplained weight gain or loss 
  • Wheezing, coughing
  • Swelling in the feet and ankles
  • Skin lesions, discolored patches of skin, thin skin
  • High blood glucose levels (frequent urination, increased thirst, increased hunger)
  • Low blood glucose levels (shakiness, dizziness, sweating, fainting)

NETs often don’t cause symptoms early in the disease process. When symptoms are present, they may be similar to those caused by more common conditions. As a result, NETs are sometimes misdiagnosed as irritable bowel syndrome (IBS). However, with IBS, abdominal discomfort is usually relieved by going to the bathroom.

Symptoms of functional neuroendocrine tumors

Because functional tumors produce excess hormones, symptoms are related to hormone production—either because the tumor cells have entered the bloodstream or because your body can no longer break down the high levels of hormones caused by the tumor.

Generally, these symptoms may include:

  • Diarrhea
  • Skin flushing or rash
  • Fluctuations in blood pressure
  • Dizziness or shakiness
  • Heart issues such as fast heartbeat
  • Shortness of breath or wheezing

Stress, alcohol use and intense exercise may exacerbate these symptoms.

Certain types of NETs present symptoms specific to their location. For example, lung NETs are less likely to be functional tumors, so they don’t tend to cause symptoms based on hormone production as compared with gastrointestinal NETs.

Below, find some examples of symptoms specific to different locations in the body.

Functional lung NETs

When functional lung NETs do cause hormone-related symptoms, these may include, among others:

  • Shortness of breath
  • Weakness
  • Abnormal heartbeat

Functional gastrointestinal tract NETs

Some symptoms include:

  • Bloating
  • Abdominal pain
  • Diarrhea

Functional pancreatic NETs

The pancreas is an organ that produces several hormones, so when an NET develops in the pancreas, the production of certain hormones may be affected.

  • If an NET of the pancreas leads to high levels of the hormone gastrin, it may cause:
    • Stomach ulcers
    • Abdominal pain
    • Acid reflux
    • Diarrhea
  • If an NET of the pancreas leads to high levels of insulin, the main symptom it may cause is low blood sugar. This may lead to:
    • Blurry vision
    • Headache
    • Dizziness and shaking
    • Weakness
    • Confusion
    • Hunger
  • High levels of the hormone glucagon may cause a rash on the face, legs or stomach. It may also cause high blood sugar, which may lead to:
    • Headache
    • Dry mouth
    • Hunger
    • Weakness
  • High glucagon levels may also cause blood clots and their related symptoms:
    • Shortness of breath
    • Cough or chest pain
    • Swelling in the area around the clot
    • Diarrhea
  • Increased levels of vasoactive intestinal peptide (VIP) may cause:
    • Dehydration
    • Diarrhea
    • Abdominal cramps
    • Low levels of potassium in the blood, which may lead toweak muscles, aching or cramping, frequent urination, thirst or a rapid heartbeat
  • A pancreatic NET that results in too much somatostatin may cause:
    • High blood sugar
    • Diarrhea
    • Gallstones
    • Jaundice (yellowing of the skin and eyes)

Symptoms of nonfunctional neuroendocrine tumors

As they grow larger, nonfunctional tumors that aren’t producing excess hormones may cause symptoms based on which nearby tissues and structures they’re affecting.

Nonfunctional lung NETs

A nonfunctional NET in the lung may produce symptoms similar to pneumonia, such as:

  • Difficulty breathing
  • Chest pain
  • Wheezing

It may also lead to a bloody cough.

Nonfunctional gastrointestinal tract NETs

These NETs may cause a variety of GI-related issues such as:

  • Diarrhea
  • Vomiting and nausea
  • Constipation
  • Abdominal pain
  • Dark bowel movements caused by blood in the stool

They also may cause unexplained weight loss, a rash or fatigue.

Nonfunctional NETs of the appendix

A nonfunctional NET of the appendix may cause symptoms similar to appendicitis, including the telltale sign of pain in the abdomen. NETs in the appendix are often found as a result of surgery to treat apparent appendicitis.

Nonfunctional pancreatic NETs

A nonfunctional NET of the pancreas may cause gastrointestinal issues such as:

  • Diarrhea
  • Upset stomach

It may also be felt as a lump in the abdomen, or lead to pain in the abdomen or back.

What to do if you notice symptoms

Because most NET patients are diagnosed at an advanced stage, it’s important to let your doctor know if you notice new or persisting symptoms or changes in your body. NETs can be especially tricky to diagnose because, if they do cause symptoms, those symptoms tend to resemble other conditions. Getting a full picture of your symptoms is key.

After you describe your symptoms, your doctor may decide to order tests in order to make a diagnosis. These may include:

Next topic: What are the types of neuroendocrine tumors?

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