Carcinoid Syndrome: Symptoms, Causes, Diagnosis, and Treatment of This Rare NET Complication
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick answer
Carcinoid syndrome is a rare condition caused by neuroendocrine tumors (NETs) that release large amounts of serotonin and other hormones into the bloodstream [1] [2]. Its signature symptoms are flushing, wheezing and abdominal cramping with explosive diarrhea [1] [2]. About 1 in 5 people with NETs develop it [1]. Diagnosis uses hormone tests and imaging, and treatment targets the tumors [1].
What the research says
According to PubMed:
Somatostatin analogues give substantial symptom relief, and refractory symptoms have options. A systematic review searched 233 unique records and included 12 prospective trials of carcinoid syndrome treatments. Somatostatin analogues provided substantial symptom relief; for symptoms that persisted, a higher analogue dose or adding telotristat ethyl were valuable options, and treatments were generally well tolerated with few serious treatment-related adverse events (Wolin & Benson, Oncology, 2019) [5].
Telotristat ethyl was linked to weight gain in a phase III trial. In the placebo-controlled TELESTAR trial of 135 patients whose symptoms were not controlled on somatostatin analogues, weight gain of 3% or more at week 12 occurred in 5.1% of those on placebo, 17.1% on telotristat ethyl 250 mg, and 32.5% on 500 mg three times daily (P = 0.0017) — alongside reduced diarrhea severity (Weickert et al., Clinical Therapeutics, 2018) [6].
Screening for carcinoid heart disease and preventing crisis matter. A clinical review advises screening for carcinoid heart disease because early intervention prolongs survival, and notes that carcinoid crisis — mostly described during surgery, anaesthesia, chemotherapy, and radiological procedures — may be prevented with octreotide (Clement et al., Journal of Oncology, 2020) [2].
Study details are from PubMed abstracts.
What is carcinoid syndrome?
Carcinoid syndrome is a rare condition that happens if you have neuroendocrine tumors. Neuroendocrine tumors (NETs) are rare tumors that start in specialized cells in your neuroendocrine system [1].
NETs develop when your neuroendocrine cells begin to rapidly divide and multiply, creating tumors that release unusually large amounts of serotonin and other substances [1]. When that happens, you develop carcinoid syndrome symptoms. Sometimes, a carcinoid syndrome diagnosis is the first indication you have a neuroendocrine tumor [1].
Very rarely, people with carcinoid syndrome have carcinoid crises — a potentially life-threatening condition that can happen if your carcinoid syndrome goes undiagnosed or untreated [1].
Is carcinoid syndrome common?
No, it's not. One study suggests 1 in 5 people with neuroendocrine tumors (NETs) have carcinoid syndrome, and NETs affect about 5 in 100,000 people in the United States [1].
What are carcinoid syndrome symptoms?
Studies suggest the most common carcinoid syndrome symptoms include flushing of the head and neck, wheezing, shortness of breath, abdominal cramping and frequent diarrhea [1] [2].
Uncomfortable flushing of your head and neck
Wheezing and shortness of breath (dyspnea)
Abdominal cramping and explosive, frequent diarrhea
Fatty poops that smell bad
Edema (swelling) of your feet and legs, which can be a symptom of heart failure
Loss of interest in sex or erectile dysfunction
Jaundice, which is when your skin and the whites of your eyes turn yellow
Dizziness or feeling faint, which can be a sign of low blood pressure
Feeling like your heart is racing
What causes carcinoid syndrome?
Carcinoid syndrome happens if you have neuroendocrine tumors. This refers to symptoms that develop from tumors in specialized cells in your neuroendocrine system that make and release hormones. While you can have NETs in your gastrointestinal tract, lungs and pancreas, carcinoid syndrome typically happens when NETs in your gastrointestinal tract or lungs flood your system with hormones [1].
What are the risk factors?
The most common risk factor is having a neuroendocrine tumor in your gastrointestinal tract or your lungs [1].
Key fact | What the research says |
How many people with NETs get it | About 1 in 5 people with NETs have carcinoid syndrome |
How common NETs are | NETs affect about 5 in 100,000 people in the United States |
Where the tumors usually are | The gastrointestinal tract or the lungs |
First clue? | Sometimes the syndrome is the first sign a NET exists |
What are the complications of carcinoid syndrome?
Carcinoid syndrome may cause several kinds of complications, among them carcinoid crisis, an extremely rare but life-threatening condition. Other complications include:
Carcinoid heart disease: A rare but potentially life-threatening complication that happens when neuroendocrine tumors release hormones that affect the linings in your heart chambers, valves and blood vessels. It may lead to heart failure [1] [2].
Mesenteric fibrosis: NETs may cause inflammation and scarring of your mesentery, which is a fold of tissue that attaches your intestines to the wall of your belly [1].
Depression: Carcinoid syndrome may affect your body's ability to process tryptophan [1], an essential amino acid that helps to make serotonin. Because serotonin is a brain chemical that manages central nervous system processes like mood, behavior and sleep, this disruption can contribute to depression.
What is a carcinoid crisis?
A carcinoid crisis is an extremely rare but life-threatening condition. Triggers include surgery or other medical procedures, or traumatic events like an injury from an accident [1] [4]. Symptoms include wide changes in blood pressure, including low blood pressure (hypotension); severe flushing; shortness of breath (dyspnea); and confusion [1].
People with carcinoid syndrome or a neuroendocrine tumor should carry a card listing their medical condition in case they need emergency medical care [1]. Likewise, people with carcinoid syndrome or an NET who are planning to have surgery should make sure their providers know about their condition. Providers can administer medication before and during surgery to reduce carcinoid crisis risk [1] [2].
How is carcinoid syndrome diagnosed?
Healthcare providers may use the following tests to diagnose carcinoid syndrome [1]:
Test | What it does |
Urine test | Checks on certain hormone levels |
Physical exam and medical history | Many symptoms resemble less serious illnesses; the provider asks about specific symptoms, how long you've had them, and whether they're worsening |
Blood tests | Check the amounts of substances your organs and tissues release into your blood; spikes or falls may signal disease |
Neuroendocrine PET scan | Tracks neuroendocrine tumors with a dye called Gallium 68 dotatate |
CT scan | Uses X-rays and a computer to produce 3D images of organs and bones |
Ultrasound | Uses sound waves to develop images of organs and bones |
MRI | Uses a computer, radio waves and a large magnet to create images of the inside of your body |
Endoscopy | A provider inserts a long thin tube with a camera and a light into your body |
How is carcinoid syndrome treated?
Carcinoid syndrome is treated by treating the neuroendocrine tumors that cause it [1]. Treatments include:
Treatment | How it works |
Surgery | Removes or reduces the size of the neuroendocrine tumors |
Somatostatin analogs | Drugs that may stop your body from making too many hormones and may slow down tumor growth when cancer cells spread to other parts of your body [1] |
Targeted therapy | Uses drugs that target certain genes or proteins to kill cancer cells |
Chemotherapy | Uses drugs that destroy cancer cells |
Embolization | Kills tumors by blocking or closing a blood vessel that feeds the tumor |
Can carcinoid syndrome be prevented?
No, it can't be prevented. Carcinoid syndrome is linked to neuroendocrine tumors, and as there isn't a known way to prevent NETs, there's no way to prevent its symptoms [1].
How can people live with carcinoid syndrome?
Living with carcinoid syndrome means telling your provider about symptoms, managing flushing, wheezing and diarrhea, and going to the ER for problems like chest pain or severe diarrhea.
How do I take care of myself?
If you have carcinoid syndrome, you probably also have a neuroendocrine tumor. If you have carcinoid syndrome symptoms, tell your healthcare provider. They'll be able to assess your situation and recommend tests to determine if you have an NET.
The three main carcinoid syndrome symptoms are flushing, wheezing and diarrhea. Here are some suggestions for managing the main symptoms:
Symptom | Self-care tips |
Flushing | A reaction of your nervous system to physical or emotional stress. Ease it with deep breaths, cooling your face and chest with a damp cloth, or fresh air. Avoiding alcohol can reduce flushing [1]. |
Wheezing | Try drinking herbal tea, or use an inhaler or a vaporizer to help your breathing. If you smoke, try to stop — smoking irritates your airways. |
Diarrhea | Talk to your healthcare provider about ways to reduce its frequency and severity. There are medications specifically designed to slow down diarrhea from carcinoid syndrome [1]. |
When should I see my healthcare provider?
You should see your healthcare provider if your carcinoid syndrome symptoms get worse.
When should I go to the emergency room?
Emergency: Go to the emergency room if:
You're having heart palpitations or chest pain
You have severe diarrhea that's lasted several days
You have severe stomach pain
You feel faint
You have acute flushing of your face, neck and chest [1]
What questions should I ask my healthcare provider?
Carcinoid syndrome might be a sign you have a neuroendocrine tumor. While you'll have questions about carcinoid syndrome, you'll probably have more questions about NETs. Here are some questions you might want to ask:
If I have carcinoid syndrome, how do I find out if I have a neuroendocrine tumor?
If I have a tumor, where is it located in my body?
What's the treatment for my tumor?
What are the treatment side effects?
Can you cure the neuroendocrine tumor that caused my carcinoid syndrome?
Can carcinoid syndrome come back after you treat my neuroendocrine tumor?
Conclusion
Carcinoid syndrome is a rare chain reaction: a neuroendocrine tumor overproduces serotonin and other hormones, and the body answers with flushing, wheezing, diarrhea, and a handful of harder-to-spot signs like jaundice, edema, and a racing heart. About 1 in 5 people with NETs develop it — and for some, the syndrome is the very first clue that a tumor exists. The encouraging part is that treating the tumors treats the syndrome, with options ranging from surgery to hormone-blocking drugs, targeted therapy, chemotherapy, and embolization. Because a carcinoid crisis can be life-threatening, stay ahead of it: carry a medical-condition card, make sure every provider knows about your NET before any surgery, and go to the ER for palpitations, chest pain, severe multi-day diarrhea, severe stomach pain, faintness, or sudden severe flushing.
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Frequently asked questions
What is carcinoid syndrome?
Carcinoid syndrome is a rare condition caused by neuroendocrine tumors (NETs) — tumors that start in specialized hormone-making cells of the neuroendocrine system and release unusually large amounts of serotonin and other substances into the body.
Is carcinoid syndrome common?
No. About 1 in 5 people with NETs have it, and NETs themselves affect roughly 5 in 100,000 people in the United States.
What are the main symptoms?
The three signature symptoms are flushing of the head and neck, wheezing with shortness of breath, and abdominal cramping with explosive, frequent diarrhea. Other symptoms include fatty stools, swollen feet and legs, erectile dysfunction, jaundice, dizziness, and a racing heart.
What causes carcinoid syndrome?
Neuroendocrine tumors in the gastrointestinal tract or lungs that flood the body with hormones, especially serotonin.
Who is at risk?
The most common risk factor is having a neuroendocrine tumor in the gastrointestinal tract or the lungs.
Can carcinoid syndrome be the first sign of a tumor?
Yes — sometimes a carcinoid syndrome diagnosis is the first indication you have a neuroendocrine tumor.
What is a carcinoid crisis?
An extremely rare but life-threatening complication triggered by surgery, medical procedures, or trauma, causing wide blood pressure changes (including low blood pressure), severe flushing, shortness of breath, and confusion.
How do I reduce the risk of a carcinoid crisis?
Carry a card listing your medical condition for emergencies, and make sure providers know about your NET before any surgery — they can give medication before and during the procedure to reduce risk.
What complications can carcinoid syndrome cause?
Carcinoid heart disease (hormones affect the linings of heart chambers, valves and blood vessels and can lead to heart failure), mesenteric fibrosis (inflammation and scarring of the tissue attaching intestines to the belly wall), and depression (from disrupted tryptophan processing, which affects serotonin production).
How is it diagnosed?
With urine and blood hormone tests, a neuroendocrine PET scan using Gallium 68 dotatate dye, CT scan, ultrasound, MRI, and endoscopy.
How is carcinoid syndrome treated?
By treating the underlying tumors — with surgery, somatostatin analogs (hormone-blocking drugs that may slow tumor growth), targeted therapy, chemotherapy, or embolization (blocking the blood vessel feeding the tumor).
Can it be prevented?
No. There's no known way to prevent NETs, so there's no way to prevent the syndrome's symptoms.
How can I manage symptoms at home?
For flushing: deep breaths, a damp cloth on the face and chest, fresh air, and avoiding alcohol. For wheezing: herbal tea, an inhaler or vaporizer, and quitting smoking. For diarrhea: ask your provider about medications made to slow carcinoid-related diarrhea.
When should I go to the ER?
For heart palpitations or chest pain, severe diarrhea lasting several days, severe stomach pain, feeling faint, or acute flushing of the face, neck and chest.
What questions should I ask my doctor?
How do I find out if I have a NET? Where is the tumor located? What's the treatment and its side effects? Can the tumor be cured? Can the syndrome come back after treatment?
Related reading
Peptide Receptor Radionuclide Therapy (PRRT): How It Works explains PRRT for neuroendocrine tumors.
This article is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions about a medical condition. Never disregard professional medical advice or delay seeking care because of something you have read here.
References
Cleveland Clinic. Carcinoid Syndrome. Cleveland Clinic. Medically reviewed; last updated June 14, 2023. https://my.clevelandclinic.org/health/diseases/22103-carcinoid-syndrome
Clement D, Ramage J, Srirajaskanthan R. Update on pathophysiology, treatment, and complications of carcinoid syndrome. J Oncol. 2020;2020:8341426. PMID 32322270. https://doi.org/10.1155/2020/8341426
Koumarianou A, Daskalakis K, Tsoli M, et al. Efficacy, safety and unmet needs of evolving medical treatments for carcinoid syndrome. J Neuroendocrinol. 2022;34(7):e13174. PMID 35794780. https://doi.org/10.1111/jne.13174
Maxwell JE, Naraev B, Halperin DM, et al. Shifting paradigms in the pathophysiology and treatment of carcinoid crisis. Ann Surg Oncol. 2022;29(5):3072-3084. PMID 35165817. https://doi.org/10.1245/s10434-022-11371-0
Wolin EM, Benson AB III. Systemic treatment options for carcinoid syndrome: a systematic review. Oncology. 2019;96(6):273-289. PMID 31018209. https://doi.org/10.1159/000499049
Weickert MO, Kaltsas G, Hörsch D, et al. Changes in weight associated with telotristat ethyl in the treatment of carcinoid syndrome. Clin Ther. 2018;40(6):952-962.e2. PMID 29724499. https://doi.org/10.1016/j.clinthera.2018.04.006
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