What Are the Symptoms of Carcinoid Syndrome?

Carcinoid syndrome is a collection of symptoms caused by a tumor releasing excessive amounts of hormones, most notably serotonin, into your bloodstream ^[1]. While often discussed alongside endocrine gland tumors, these tumors develop from specialized cells called neuroendocrine cells that are found throughout the body, most commonly in your digestive tract or lungs. While many neuroendocrine tumors do not produce hormones, those that do can trigger a specific set of disruptive physical reactions known as carcinoid syndrome ^[2][3].

The Classic Symptoms of Carcinoid Syndrome

The symptoms of carcinoid syndrome can vary from person to person, but they often include a classic triad of issues ^[3]:

• Sudden Skin Flushing: You may experience a sudden, intense redness and feeling of warmth, usually on your face, neck, or upper chest ^[4]. This flushing can happen spontaneously or be triggered by stress, exercise, alcohol, or eating certain trigger foods (such as heavy meals or foods high in amines, like aged cheeses).
• Severe Diarrhea: Frequent, watery bowel movements are a hallmark of carcinoid syndrome ^[4]. This diarrhea can be debilitating and is often accompanied by abdominal cramping or pain ^[3]. Living with severe diarrhea can be incredibly disruptive and emotionally exhausting, but knowing the cause is the first step toward getting treatments that can help.
• Wheezing and Shortness of Breath: You might experience a whistling sound when you breathe or feel like you cannot catch your breath, similar to asthma symptoms ^[4].

In addition to these symptoms, because the tumor uses up the body’s supply of tryptophan to create all this excess serotonin, some people can develop a vitamin B3 (niacin) deficiency known as pellagra ^[4].

How Tumors Cause These Symptoms

In a healthy body, the liver breaks down excess serotonin and other chemicals ^[5]. However, if a neuroendocrine tumor has spread (metastasized) to the liver or is located in a way that allows its hormones to bypass the liver’s filtering process, these active chemicals enter your general blood circulation directly ^[5][3].

When large amounts of serotonin and other vasoactive substances (chemicals that affect your blood vessels) flood your system, they cause the blood vessels in your skin to expand (triggering flushing), stimulate the intestines to move too quickly (causing diarrhea), and narrow the airways in your lungs (leading to wheezing) ^[1][6].

Long-Term Complications to Watch For

If left untreated over a long period, the constant high levels of serotonin in the blood can lead to a more serious complication known as carcinoid heart disease ^[7][3]. This condition occurs when scar tissue builds up on the valves of the heart, particularly on the right side, making it harder for the heart to pump blood effectively ^[8][9]. Your doctor can actively monitor for this by ordering regular echocardiograms (ultrasounds of the heart).

You must also be aware of the risk of a carcinoid crisis, a severe, sudden, and potentially life-threatening release of hormones ^[10]. This is most often triggered by physical stress such as surgery, anesthesia, or tumor biopsies ^[11]. It is vital to tell any surgeon or anesthesiologist about your condition beforehand so they can monitor you closely and administer medications to prevent a crisis ^[12].

Next Steps and Diagnosis

If you are experiencing the symptoms of carcinoid syndrome, it is important to communicate them clearly to your care team. They can diagnose the condition by testing your hormone levels, often using a 24-hour 5-HIAA urine test, which measures the breakdown products of serotonin over a full day ^[13][14].

Once diagnosed, your team can prescribe treatments specifically designed to block hormone production, such as somatostatin analogs (SSAs) ^[15][16]. These medications can significantly reduce your daily symptoms and help protect your heart from long-term damage.