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Health condition · Clinically reviewed

Carcinoid syndrome, flushing, diarrhoea and the modern NET pathway.

A rare but treatable syndrome from vasoactive hormones released by neuroendocrine tumours. Specialist NET centres, somatostatin analogues and PRRT have transformed what is possible.

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A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a UK NET clinician before publication.

  • 02

    Sourced from guidance

    Checked against ENETS, UKINETS and NCCN neuroendocrine tumour guidance, cited at the end.

  • 03

    Current for 2026

    Reflects modern UK practice, including somatostatin analogues, telotristat, PRRT and specialist NET-centre pathways.

Key facts

Carcinoid syndrome at a glance.

The essentials, in plain English: what it is, why it happens, the key test and the foundations of UK NET treatment.

  • What it is

    A cluster of symptoms caused by vasoactive substances (serotonin, tachykinins, histamine, bradykinin, prostaglandins) released by a carcinoid tumour.

  • When it appears

    Usually only once the tumour has spread to the liver, or when a primary drains directly into the systemic circulation (bronchial, ovarian, retroperitoneal).

  • How common

    Only around 10 per cent of carcinoid tumours produce the syndrome, but it is the most recognisable presentation of neuroendocrine disease.

  • Classic triad

    Episodic flushing, secretory diarrhoea and, over time, right-sided valvular heart disease (Hedinger syndrome).

  • Key test

    24-hour urinary 5-HIAA plus plasma chromogranin A, supported by 68Ga-DOTATATE PET-CT imaging.

  • Foundation therapy

    Long-acting somatostatin analogues (octreotide LAR or lanreotide autogel) control symptoms and slow tumour growth.

Why this guide matters

A rare cancer, a specialist pathway.

Neuroendocrine tumours are frequently missed for years. Getting to a specialist NET centre changes symptoms, quality of life and long-term outcomes.

  • Somatostatin analogues are the backbone

    Monthly octreotide LAR or lanreotide autogel controls flushing and diarrhoea and slows tumour growth, evidenced by the PROMID and CLARINET trials.

  • Carcinoid heart disease is preventable

    Regular echo and NT-proBNP screening, plus early control of serotonin release, protect the tricuspid and pulmonary valves from irreversible fibrosis.

  • PRRT has transformed outcomes

    For progressive metastatic SSTR-positive NET, 177Lu-DOTATATE (Lutathera) offers durable disease control and is delivered at UK specialist NET centres.

How the diagnosis is made

From first flush to a clear NET plan.

The steps a UK GP, gastroenterologist and specialist NET centre will normally follow, in order, so you know what to expect and why.

  1. 01

    Assessing

    Symptom history and triggers

    A careful account of flushing episodes, stool frequency, wheeze and known triggers (alcohol, spicy food, stress, coffee, serotonin-rich foods).

  2. 02

    Assessing

    24-hour urinary 5-HIAA

    The single most useful test. A 24-hour urine collection measures serotonin metabolite, with a low-serotonin diet for 48 hours beforehand.

  3. 03

    Assessing

    Chromogranin A and NET markers

    Plasma chromogranin A, NSE and (selectively) pancreastatin, serotonin, histamine and gastrin, plus NT-proBNP to screen the heart.

  4. 04

    Confirming

    Cross-sectional imaging

    CT chest, abdomen and pelvis to identify the primary tumour, liver metastases and nodal disease.

  5. 05

    Confirming

    Somatostatin receptor PET-CT

    68Ga-DOTATATE PET-CT is the most sensitive scan for well-differentiated NET. 111In-octreoscan is an alternative where DOTATATE is unavailable.

  6. 06

    Confirming

    Liver MRI and echocardiogram

    MRI liver clarifies metastatic burden. Transthoracic echo screens for carcinoid heart disease, with right heart catheterisation in selected cases.

  7. 07

    Planning

    Biopsy and MDT

    Histology of the primary or liver metastases, with chromogranin, synaptophysin and Ki-67 grading, discussed at a specialist NET MDT.

Typical timeline: a first suspicion to a settled NET-centre plan in weeks, sometimes months, but always through an MDT.

Symptoms

What carcinoid syndrome looks like.

The classic mix of flushing, diarrhoea, wheeze and right-heart strain, plus the features that mean it is time to escalate care.

  • Episodic flushing

    Dry flushing of the face, neck and upper trunk, unlike the sweaty flushing of the menopause. Often triggered by alcohol, food or stress.

  • Secretory diarrhoea

    Watery, non-bloody stools, sometimes 20 to 30 times a day. Persists on fasting and disturbs sleep.

  • Bronchospasm and wheeze

    An asthma-like wheeze during flushing episodes, driven by vasoactive mediators rather than airway disease.

  • Carcinoid heart disease

    Right-sided valvular fibrosis (tricuspid regurgitation, pulmonary stenosis) causing breathlessness, oedema and hepatomegaly.

  • Pellagra-like dermatitis

    Rough, pigmented skin over sun-exposed areas from niacin deficiency, as tryptophan is diverted into serotonin production.

  • Telangiectasia and cyanosis

    Fine facial telangiectasia and a bluish cast to the cheeks develop with chronic flushing over months to years.

  • Weight loss and fatigue

    Chronic diarrhoea, poor absorption and cytokine effects lead to weight loss and a heavy fatigue that outlasts the flushes.

  • Red flag - carcinoid crisis

    Profound hypotension, arrhythmia, severe bronchospasm and flushing, often provoked by anaesthesia, surgery or tumour handling.

Treatment

How carcinoid syndrome is treated in the UK.

Somatostatin analogues first, telotristat for stubborn diarrhoea, and the full arsenal of surgery, liver-directed therapy, PRRT and targeted or cytotoxic drugs for the tumour itself.

  • Somatostatin analogue (long-acting)

    Octreotide LAR (Sandostatin) or lanreotide autogel (Somatuline) monthly. First-line for flushing, diarrhoea and slowing tumour growth (PROMID, CLARINET).

  • Short-acting octreotide

    Subcutaneous octreotide for breakthrough symptoms and peri-procedural cover to reduce the risk of carcinoid crisis.

  • Telotristat ethyl (Xermelo)

    Oral tryptophan hydroxylase inhibitor for diarrhoea that persists despite a somatostatin analogue. Detail on our /treatments/telotristat-ethyl-clinic/ page.

  • Interferon-alpha

    A selective add-on where somatostatin analogues alone do not control symptoms, particularly in slowly progressive disease.

  • Dietary and niacin support

    Small frequent meals, avoiding known triggers and niacin (vitamin B3) supplementation to counter pellagra-like skin changes.

  • Surgery and hepatic debulking

    Resection of the primary tumour and liver metastasectomy or debulking at specialist HPB and NET centres, where feasible.

  • Liver-directed therapy

    TACE, TARE with Y90 (see /treatments/tare-y90-selective-internal-radiation/), radiofrequency or microwave ablation for liver-dominant disease.

  • PRRT with 177Lu-DOTATATE

    Lutathera peptide receptor radionuclide therapy for progressive metastatic well-differentiated SSTR-positive NET (NETTER-1), at UK specialist NET centres.

Also considered

Targeted therapy, chemotherapy, cardiac care and mandatory perioperative octreotide.

Everolimus (mTOR inhibitor) and sunitinib (VEGFR inhibitor) have roles in pancreatic and selected GI NETs. Capecitabine-temozolomide, streptozotocin-5FU and etoposide-platinum are used for higher-grade disease. Carcinoid heart disease is managed with diuretics, careful fluid balance and, where appropriate, tricuspid and pulmonary valve replacement at specialist cardiac centres. Perioperative intravenous octreotide is mandatory to prevent carcinoid crisis, coordinated with a specialist NET anaesthetist and an agreed NET protocol.

What this guide is based on

The sources behind every claim on this page.

UK, European and North American NET guidance and the pivotal trials that shape modern practice, current at the time of last review.

Key references

Guidelines and pivotal trials we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your NET MDT knows your imaging, histology and cardiac status and can tell you which parts apply to you. If in doubt, contact your NET specialist nurse.

  • ENETS. Consensus guidelines for the management of patients with functional neuroendocrine tumours and carcinoid syndrome.

  • UKINETS. UK and Ireland Neuroendocrine Tumour Society guidance for gastroenteropancreatic and lung NETs.

  • NCCN. Neuroendocrine and adrenal tumours clinical practice guidelines in oncology.

  • NICE. Lutetium (177Lu) oxodotreotide for treating unresectable or metastatic neuroendocrine tumours.

  • NETTER-1 trial. 177Lu-DOTATATE in midgut neuroendocrine tumours (N Engl J Med).

  • MHRA / eMC. Summary of Product Characteristics for octreotide, lanreotide and telotristat ethyl.

Red flags

When to seek urgent NET-centre input.

Most day-to-day symptoms settle on somatostatin analogues. These are the situations that do not, and where specialist review cannot wait.

  • Carcinoid crisis

    Life-threatening hypotension, arrhythmia and bronchospasm. Requires immediate octreotide 50 to 100 micrograms per hour intravenously and specialist critical care input.

  • Peri-operative and peri-procedural risk

    Anaesthesia, surgery, biopsy, embolisation and chemotherapy can all trigger crisis. Octreotide cover and a specialist NET anaesthetist are mandatory.

  • New or worsening breathlessness

    Suggests progression of carcinoid heart disease or new pulmonary metastases. Needs urgent echo, NT-proBNP and specialist cardiology review.

  • Right heart failure signs

    Rising jugular venous pressure, hepatomegaly, ascites or peripheral oedema warrant prompt cardiology and NET MDT input.

  • Severe uncontrolled diarrhoea

    More than 8 to 10 stools a day despite treatment risks dehydration, electrolyte loss and acute kidney injury. Consider inpatient stabilisation.

  • Sudden severe flushing with syncope

    May herald crisis. Attend the emergency department and inform the team about the neuroendocrine diagnosis.

  • Rapid weight loss or jaundice

    Could indicate progressive liver metastases or biliary obstruction. Needs urgent imaging and MDT review.

  • New neurological symptoms

    Bone metastases or, rarely, brain metastases require prompt imaging and referral to specialist NET services.

  • Pregnancy planning

    Somatostatin analogues, PRRT and many NET treatments require careful counselling. Speak to the NET team before conception.

Living with it

A rare cancer, with a modern playbook.

Four things that make the biggest difference day to day: knowing your triggers, staying under a specialist NET centre, carrying a NET emergency card, and drawing on patient support.

A quiet reminder

Steady MDT care outperforms heroic single treatments.

NET disease is a long game. Consistent contact with the NET specialist nurse, regular scans and honest symptom reporting matter more than any one intervention.

  1. 01 Triggers

    Know your flush triggers

    Alcohol, spicy food, coffee, stress and serotonin-rich foods (bananas, walnuts, tomatoes, pineapple) commonly provoke flushing. A simple diary helps.

  2. 02 Team

    Stay under a specialist NET centre

    UK NET services (including Royal Free, Christie, University College, Newcastle, Sheffield, Basingstoke and Liverpool) offer MDT care, PRRT and specialist NET nurse support.

  3. 03 Cards

    Carry a NET emergency card

    A card or letter with your diagnosis, octreotide dose and NET-centre contact details is invaluable if you need unplanned surgery or anaesthesia.

  4. 04 Support

    Use patient support networks

    The NET Patient Foundation offers information, buddy schemes and helplines. You are not on your own with a rare cancer diagnosis.

Frequently asked

Everything we get asked about carcinoid syndrome.

Quick answers on 5-HIAA testing, somatostatin analogues, carcinoid heart disease, telotristat and PRRT.

  • What is carcinoid syndrome?

    Carcinoid syndrome is a cluster of symptoms caused by vasoactive substances (mainly serotonin, but also tachykinins, histamine, bradykinin and prostaglandins) released by a carcinoid tumour. It usually appears when the tumour has spread to the liver or arises somewhere that drains directly into the systemic circulation, such as the lung or ovary.

  • Why does it only happen in some carcinoid tumours?

    Only around 10 per cent of carcinoid tumours produce the syndrome. Most of the hormones released by a bowel primary are broken down as blood passes through the liver. Symptoms usually appear only when liver metastases bypass that first-pass metabolism, or when the primary is bronchial, ovarian or retroperitoneal.

  • How is the diagnosis confirmed?

    The core biochemical test is a 24-hour urinary 5-HIAA (a serotonin metabolite), supported by plasma chromogranin A. Imaging with CT and a 68Ga-DOTATATE PET-CT localises the tumour, and an echocardiogram screens for carcinoid heart disease. A biopsy confirms the histology and Ki-67 grade.

  • What is carcinoid heart disease?

    Also known as Hedinger syndrome, it is fibrotic thickening of the right-sided heart valves (tricuspid regurgitation and pulmonary stenosis) driven by serotonin exposure. It is a major cause of morbidity and mortality and is screened for with regular echocardiograms and NT-proBNP.

  • What is a carcinoid crisis and how is it prevented?

    Carcinoid crisis is a life-threatening surge of profound hypotension, arrhythmia, bronchospasm and flushing, most often triggered by anaesthesia, surgery, tumour handling, embolisation or chemotherapy. It is prevented by intravenous octreotide (typically 50 to 100 micrograms per hour) started before the procedure, given by a specialist NET anaesthetist.

  • What treatments actually control the symptoms?

    Long-acting somatostatin analogues (octreotide LAR or lanreotide autogel) are the mainstay. Telotristat ethyl helps refractory diarrhoea. Liver-directed treatments (TACE, TARE Y90, ablation), surgery and PRRT with 177Lu-DOTATATE address the underlying tumour. Care is coordinated at a specialist NET centre.

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