- Clinical science
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.
- Carcinoid tumors are neuroendocrine tumors.
- 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).
Serotonin can reach systemic circulation under the following conditions:
- Intestinal carcinoid tumors with liver metastases
- Extraintestinal carcinoid tumors
- ↑ serotonin in systemic circulation leads to
- May cause pellagra (niacin deficiency) due to increased serotonin metabolism
- Serotonin can reach systemic circulation under the following conditions:
- Abdominal pain
- Carcinoid syndrome
Carcinoid heart disease
- Tricuspid insufficiency and/or
- Possible pellagra (niacin deficiency)
- Biochemistry tests
- Biopsy (with histology and immunohistochemistry)
- Irritable bowel syndrome
- Celiac disease
- Definition: neuroendocrine tumor that secretes excess VIP (vasoactive intestinal polypeptide)
- Excess VIP → increases relaxation of gastric and intestinal smooth muscles and adenylate cyclase (cAMP) activity (similar to cholera toxin) → secretory diarrhea and inhibition of gastric acid production
- VIP also stimulates vasodilation, bone resorption, and glycogenolysis
- Associated with (5% of cases)
- Tumor location: The primary tumor is most frequently found in the pancreas.
- Clinical features
- Treatment: tumor resection or octreotide
The differential diagnoses listed here are not exhaustive.
- Operable disease
- Inoperable disease