What is Carcinoid Syndrome?
Carcinoid Syndrome (CS) is a group of symptoms in people with neuroendocrine tumors (NETs)1
CS symptoms are caused, in part, by too much serotonin in the gut.1 Some of the most common symptoms of CS are diarrhea, facial flushing, wheezing, and tissue fibrosis or heart valve damage that could lead to carcinoid heart disease.1
What causes Carcinoid Syndrome Diarrhea (CSD)?
CSD occurs largely due to NET cells producing too much serotonin1
Serotonin: More than the “happy” hormone
Serotonin is a hormone that is made and released by cells in both the brain and the gut. It’s sometimes referred to as the “happy” hormone because serotonin produced in the brain helps regulate mood. But serotonin made in the gut plays an important role in other bodily functions, including bowel movements.
Too much of a good thing
In people with CS, serotonin levels can be significantly greater than average. An overproduction of serotonin by NET cells can lead to diarrhea, flushing, wheezing, fibrosis, and carcinoid heart disease, among other effects.1
Over time, too much serotonin may increase the amount of fluid in the gut.1 It can also speed up the function of the gut, which may cause frequent, unpredictable diarrhea.1 Even with somatostatin analog (SSA) treatment, some patients with CS continue to experience diarrhea.1
The science behind CSD
When cells grow abnormally, they form a tumor.3
When a tumor forms in the neuroendocrine system, it may produce too many hormones, like serotonin.3
Hormones are one way your body’s cells communicate with each other to help with bodily functions. For example, serotonin is a hormone that communicates with your gut to help with digestion.1
When NETs produce too much serotonin, your body’s natural serotonin levels can be thrown off balance. The extra serotonin in the gut can lead to CSD.1
Diarrhea can feel like an “eruption”
You know how diarrhea can feel. It can be sudden, frequent, urgent and last a long time. Kind of like when a volcano erupts. In your body, excess serotonin can cause an increase in the frequency of diarrhea. Reducing serotonin levels in the body may help to reduce the frequency of diarrhea.1
Talk with your doctor about serotonin and CSD
There are other factors that can lead to CSD, although higher serotonin levels normally play a role.1 Talk with your healthcare provider about whether too much serotonin could be the cause of your CSD.
Download this discussion guide to start the conversation with your doctor.
- Naraev BG, Halland M, Halperin DM, Purvis AJ, O’Dorisio TM, Halfdanarson TR. Management of diarrhea in patients with carcinoid syndrome. Pancreas. 2019;48(8):961-972.
- Rubin de Celis Ferrari AC, Glasberg J, Riechelmann RP. Carcinoid syndrome: update on the pathophysiology and treatment. Clinics. 2018;73(suppl 1):e490s. doi:10.6061/clinics/2018/e490s.
- Cancer.net. Neuroendocrine Tumors: Introduction. Updated January 2021. https://www.cancer.net/cancer-types/neuroendocrine-tumors/introduction.