Carcinoid syndrome – Diagnostics – Overview of Information and Clinical Research

Carcinoid syndrome requires careful diagnostic evaluation to confirm the presence of neuroendocrine tumors and measure the hormones causing symptoms. Understanding the available diagnostic methods can help patients and their doctors identify the condition early and develop an appropriate care plan.

Introduction: Who Should Undergo Diagnostics

If you notice unusual symptoms such as sudden flushing of your face and neck, frequent watery diarrhea, or wheezing that seems unrelated to asthma, it may be time to talk with your doctor. Carcinoid syndrome is a rare condition that occurs when special tumors called neuroendocrine tumors (or NETs) release large amounts of hormones and other substances into your bloodstream. These substances, especially one called serotonin, trigger a range of uncomfortable symptoms that can significantly affect your daily life.^[1]^[2]

Most people with carcinoid syndrome have neuroendocrine tumors that have spread to other parts of the body, particularly the liver. This is because under normal circumstances, the liver breaks down these hormones before they can cause problems. However, when tumors grow in the liver itself or when they bypass the liver’s filtering system, hormones flood into the bloodstream and cause symptoms. Carcinoid syndrome most commonly affects people who have NETs in their digestive system or lungs.^[3]^[9]

You should seek diagnostic testing if you experience repeated episodes of skin flushing that feels hot and changes your skin color from pink to purple, persistent diarrhea that occurs many times per day, or breathing difficulties that resemble asthma symptoms. Some people also notice their heart racing, swelling in their legs and ankles, or even patches of purplish spidery veins on their nose and upper lip. These symptoms can appear suddenly or worsen over time, and certain triggers like stress, exercise, or drinking alcohol may make them more intense.^[1]^[2]

It is especially important to see your doctor promptly if you notice these symptoms together or if they are disrupting your ability to function normally. Sometimes a carcinoid syndrome diagnosis is actually the first clue that someone has a neuroendocrine tumor, because the tumor itself may not have caused any other noticeable problems yet. Early diagnosis can help prevent serious complications and allow treatment to begin sooner.^[2]

⚠️ Important

People with carcinoid syndrome should carry a card listing their medical condition at all times. This is because a rare but potentially life-threatening situation called carcinoid crisis can occur, especially during surgery, medical procedures, or after traumatic injuries. Carcinoid crisis causes severe symptoms including dangerous drops in blood pressure, extreme flushing, and breathing difficulties that require immediate emergency care.^[2]^[8]

Classic Diagnostic Methods for Identifying Carcinoid Syndrome

When you visit your doctor with concerning symptoms, they will first assess your signs and symptoms carefully to rule out other possible causes of flushing and diarrhea. Many conditions can cause similar symptoms, so your doctor needs to eliminate other explanations before suspecting carcinoid syndrome. If no other causes are found and your symptoms match the pattern of carcinoid syndrome, your doctor will recommend specific tests to confirm the diagnosis.^[7]

Urine Tests

The most important diagnostic test for carcinoid syndrome is a urine test that measures a substance called 5-hydroxyindoleacetic acid, or 5-HIAA for short. This substance is what remains after your body breaks down serotonin, the hormone most commonly released by carcinoid tumors. When tumors produce too much serotonin, your body breaks it down and the 5-HIAA ends up in your urine. An unusually high level of 5-HIAA in your urine strongly suggests that your body is processing extra serotonin from a carcinoid tumor.^[7]^[9]

This test is done by collecting all of your urine over a 24-hour period. Your doctor will give you specific instructions on how to collect and store the urine samples properly. It is important to follow these instructions carefully to ensure accurate results. You may also need to repeat the test to confirm the findings or track changes over time.^[4]^[6]

Blood Tests

Blood tests can detect high levels of certain substances that carcinoid tumors release. One commonly measured substance is called chromogranin A, which is a protein that many neuroendocrine tumors produce. Elevated levels of chromogranin A in your blood can indicate the presence of a NET, although this test alone cannot confirm carcinoid syndrome because other conditions can also raise chromogranin A levels.^[6]

Another blood test measures NT-proBNP, which is a protein that helps doctors assess how well your heart is working. This test is particularly important because carcinoid syndrome can sometimes lead to a serious complication called carcinoid heart disease, where the hormones damage the heart valves and muscle. Checking NT-proBNP levels helps your doctor monitor your heart health.^[6]

Blood tests can also check for imbalances in minerals and vitamins. For example, carcinoid syndrome can affect your body’s ability to process tryptophan, an essential building block that helps make serotonin. When tumors use up too much tryptophan to make serotonin, you may become deficient in niacin, a vitamin that your body normally makes from tryptophan. Low niacin levels can cause dry, cracking skin and other problems.^[2]^[6]

Imaging Tests

Once blood and urine tests suggest carcinoid syndrome, your doctor will use imaging tests to locate the tumor and determine whether it has spread to other parts of your body. These tests create detailed pictures of the inside of your body without requiring surgery. Several different types of imaging may be used depending on your situation.^[7]

A CT scan (computed tomography scan) of your abdomen is often the first imaging test ordered because most carcinoid tumors are found in the gastrointestinal tract. The CT scan uses X-rays and computer processing to create cross-sectional images of your belly, allowing doctors to see tumors in your intestines, appendix, pancreas, or liver. This test is painless, though you may need to drink a contrast liquid or receive an injection of contrast dye to make the images clearer.^[7]

An MRI scan (magnetic resonance imaging) may be used in certain situations to get more detailed images. MRI uses powerful magnets and radio waves instead of X-rays to create pictures of soft tissues. This can be especially helpful for looking at the liver or other organs where tumors may have spread.^[7]

Nuclear medicine scans are specialized imaging tests that can locate neuroendocrine tumors throughout your body. These scans involve injecting a small amount of radioactive material that is attracted to NET cells. The radioactive material emits signals that special cameras can detect, creating images that show where tumors are located. These scans are particularly useful because they can find small tumors that other imaging tests might miss.^[7]

Endoscopy and Biopsy Procedures

To look directly inside your body and examine suspicious areas more closely, your doctor may use a thin, flexible tube equipped with a camera on the end. This instrument is called an endoscope, and the procedure is called endoscopy. Different types of endoscopy examine different parts of your body.^[7]

An upper endoscopy involves passing the scope down your throat to look inside your esophagus, stomach, and the beginning of your small intestine. A colonoscopy involves passing the scope through your rectum to examine your large intestine and can help diagnose tumors in the lower digestive tract. If lung carcinoid tumors are suspected, a bronchoscopy uses a scope passed down your throat and into your lungs to examine the airways.^[7]

During these procedures, your doctor can take small tissue samples called biopsies. A biopsy removes a tiny piece of the tumor so it can be examined under a microscope in a laboratory. This confirms whether the growth is indeed a neuroendocrine tumor and helps determine what type of tumor it is. The type of biopsy you need depends on where your tumor is located. Biopsies are essential for making a definitive diagnosis.^[7]

Diagnostics for Clinical Trial Qualification

When patients with carcinoid syndrome consider participating in clinical trials, they typically need to undergo additional testing beyond the standard diagnostic procedures. Clinical trials are research studies that test new treatments or combinations of treatments to see if they work better than current options. To ensure that the trial results are accurate and that patients are safe, researchers use strict criteria to decide who can participate.^[3]

Most clinical trials for carcinoid syndrome require confirmation that you have a neuroendocrine tumor that is causing your symptoms. This means you will need to have documented evidence from urine or blood tests showing elevated hormone levels, particularly high 5-HIAA in your urine or elevated chromogranin A in your blood. These biochemical markers prove that your body is producing excess hormones from a functioning NET.^[3]^[9]

Imaging tests are also crucial for clinical trial qualification. Researchers need to know exactly where your tumors are located, how large they are, and whether they have spread to your liver or other organs. You may need recent CT scans, MRI scans, or nuclear medicine scans performed within a certain time frame before enrolling in a trial. These images serve as a baseline that researchers can compare to later images to see if the treatment is working.^[3]

Some clinical trials specifically require that tumors have spread to the liver because carcinoid syndrome almost always occurs when NETs metastasize to the liver. Trials may exclude patients whose tumors have not spread or who have NETs in locations that rarely cause carcinoid syndrome. Understanding these requirements helps patients and doctors determine which trials might be appropriate.^[3]^[9]

Additionally, clinical trials often require testing to evaluate your overall health status and organ function. Blood tests to check your liver function, kidney function, and blood cell counts are common. Heart function tests, including echocardiograms (ultrasound images of the heart), may be needed because carcinoid syndrome can affect the heart. These tests ensure that you are healthy enough to tolerate the experimental treatment and that researchers can safely monitor any side effects.^[6]

Before enrolling in a clinical trial, you will also need a tissue sample from your tumor analyzed to determine its specific characteristics. This might include testing to see if your tumor cells have certain proteins on their surface called somatostatin receptors. Many NETs have these receptors, which is important because some treatments specifically target cells with somatostatin receptors. Knowing whether your tumor has these receptors helps determine which treatments might work for you.^[3]^[9]

Your medical team will carefully review all of your test results to see if you meet the specific eligibility criteria for any available clinical trials. Each trial has its own unique requirements based on the treatment being studied and the questions researchers are trying to answer. Your doctor can help explain which tests you need and what the results mean for your treatment options.

Prognosis and Survival Rate

Prognosis

The outlook for people with carcinoid syndrome varies considerably depending on several factors. Because carcinoid syndrome typically occurs only when neuroendocrine tumors have already spread to the liver or other parts of the body, it usually indicates more advanced disease. However, many neuroendocrine tumors grow slowly compared to other types of cancer, which means that even with spread to the liver, some patients can live for many years with proper treatment.^[1]^[3]

Several factors influence prognosis. The location where the tumor originally started matters—tumors arising from the midgut (small intestine and appendix) tend to have different characteristics than those from the foregut (stomach and lungs) or hindgut (colon and rectum). How well-differentiated the tumor cells are also affects outcomes; well-differentiated tumors tend to grow more slowly and have better prognoses than poorly differentiated ones. The extent of spread throughout the body and how well symptoms can be controlled with treatment also play important roles in determining what patients can expect.^[3]^[9]

Complications from carcinoid syndrome can affect prognosis significantly. Carcinoid heart disease, which occurs when hormones damage the heart valves, is a serious complication that can lead to heart failure if not detected and managed properly. Regular monitoring for heart problems is essential. Depression may also develop because carcinoid syndrome affects the body’s production of serotonin, a brain chemical that regulates mood. Another complication called mesenteric fibrosis, where inflammation and scarring affect the tissue that supports the intestines, can cause additional problems.^[2]^[8]

With advances in diagnosis and treatment, many people with carcinoid syndrome can experience good symptom control and maintain quality of life for extended periods. The key to a better prognosis often lies in early detection, appropriate treatment to control hormone secretion, and careful monitoring for complications. An interprofessional care team approach that includes specialists in different areas helps optimize outcomes for patients living with this rare condition.^[3]^[9]

Survival rate

Specific survival statistics for carcinoid syndrome are difficult to provide because outcomes vary widely depending on the type, location, and stage of the underlying neuroendocrine tumor. Carcinoid syndrome itself indicates that the NET has typically spread beyond its original location, usually to the liver. Because carcinoid syndrome only develops in about 20% of people with NETs, and NETs themselves are rare (affecting approximately 5 to 7 per 100,000 people annually), detailed survival data specifically for carcinoid syndrome patients is limited.^[2]^[3]

What we do know is that neuroendocrine tumors generally have better survival rates than many other types of cancer, even when they have spread. Some NETs are curable, especially if caught early, while others can be controlled for many years even when cure is not possible. The relatively slow-growing nature of many NETs means that patients can often live for extended periods with appropriate treatment and symptom management.^[1]^[3]

Your individual prognosis and likely survival depend on many personal factors that only your doctor can properly evaluate. These include the specific characteristics of your tumor, how your body responds to treatment, your overall health, and whether any complications develop. Your healthcare team is the best source of information about what you can expect based on your unique situation.

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