- 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.
- Incidence: 1.5/100,000 per year
- Bimodal distribution: 15–25 years and 65–75 years (but can occur at any age)
- Sex: ♂ > ♀ approx. (5:4.5)
Epidemiological data refers to the US, unless otherwise specified.
- Carcinoid tumors are neuroendocrine tumors that arise from amine precursor uptake and decarboxylation (APUD) cells.
- 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:
The rule of thirds for carcinoid tumors: ⅓ are multiple, ⅓ have a second malignancy, ⅓ metastasize.
- Abdominal pain
- Diarrhea and abdominal cramps (∼ 80% of cases)
Cutaneous flushing (85% of cases)
- Possible triggers: alcohol consumption, food intake, stress
- In severe cases, may be accompanied by tachycardia and fluctuating blood pressure
- Dyspnea, wheezing (asthma-like attacks) (25% of cases)
- Possible weight loss despite normal appetite
Carcinoid heart disease
- Tricuspid insufficiency and/or
- Possible pellagra (niacin deficiency)
- Biochemistry tests
- Biopsy (with histology and immunohistochemistry)
- Further diagnostics, depending on tumor location
- Irritable bowel syndrome, celiac disease
- Definition: neuroendocrine tumor that secretes excess VIP
- 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.
- Surgical resection is the treatment of choice. The exact procedure depends on the location of the tumor:
- Somatostatin analogs (e.g., octreotide) relieve symptoms
- Radiotherapy with radioactively-marked somatostatin analogs: indicated for neuroendocrine tumors expressing somatostatin receptors
- Palliative chemotherapy (not very efficient): to reduce rapid tumor progression
5-year survival rate: 70–80%
- Best survival rates in the case of localized disease, esp. appendiceal or lung carcinoids (93%)
- Poor survival rates in metastatic disease (20%–30%)
Carcinoid heart disease (CHD) → late complication in 20%–70% of metastatic carcinoids. CHD may be the direct cause of death.