• Clinical science

Carcinoid tumor


Carcinoids are small, slow-growing neuroendocrine tumors. They are most commonly located in the gastrointestinal tract and can synthesize a variety of hormones (especially serotonin). Most carcinoids are asymptomatic because most of the hormones they produce are metabolized by the first-pass effect in the liver. Carcinoid syndrome – characterized by diarrhea, flushing, dyspnea, and wheezing may occur if a serotonin-producing tumor has metastasized to the liver, bypassing first-pass metabolism. Elevated 5-HIAA in the urine helps to establish the diagnosis. Imaging techniques such as CT, MRI, and somatostatin receptor scintigraphy are used to detect the primary tumor as well as its metastases. Surgical resection is the first-line treatment. In inoperable cases, somatostatin analogs can be given.


  • Incidence: 1.5/100,000 per year
  • Bimodal distribution: 15–25 years and 65–75 years (but can occur at any age)


Epidemiological data refers to the US, unless otherwise specified.


  • Carcinoid tumors are neuroendocrine tumors.
  • Tumor location
    • Tumors appear most frequently in the gastrointestinal (GI) tract, especially in the intestines: (55% of cases)
    • Bronchopulmonary organ system: (30% of cases)
  • Carcinoid tumors can synthesize different hormones (most commonly serotonin).

The rule of thirds for carcinoid tumors: ⅓ are multiple, ⅓ have a second malignancy, ⅓ metastasize.


Clinical features

In a patient presenting with secretory diarrhea, episodic flushing, wheezing, and cardiac valvular abnormalities, consider a carcinoid tumor!References:[1][7][8][4][9][6]

Subtypes and variants


Biochemistry tests should be performed first if a carcinoid tumor is suspected. Imaging tests are then used to localize and stage the tumor.


Differential diagnoses


The differential diagnoses listed here are not exhaustive.