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Diagnosing |
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Carcinoid tumours, the most common type of gastro-entero-pancreatic neuroendocrine (GEP NE) tumour, tend to yield vague symptoms, and are often misdiagnosed as other disorders, such as irritable bowel syndrome. Also complicating diagnosis is the tumours' wide variance in onset. For carcinoid tumours of the cervix, for example, the average age of onset is 39 years; of the small intestine, 63 years; and of the rectum, 66 years. As a result, a correct diagnosis of carcinoid disease may be delayed anywhere from 2 to 20 years.6-7 (An analysis in the Surveillance, Epidemiology, and End Results [SEER] program showed that 45% of people with GEP NE tumours had metastases when they were first diagnosed.)8
Fig. 1. Adapted with permission from Vinik AI, et al. Dig Dis Sci. 1989;34(suppl 3):14S-27S
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Diagnosing GEP NE tumours
A diagnosis of GEP NE tumours may be based on the following:
- Clinical symptoms
- Tests that measure hormones, biochemical tumour markers and other markers in the body
- Imaging tests, such as computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and somatostatin receptor scintigraphy (SRS).
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Markers for GEP NE tumours
The following markers may help identify specific GEP NE tumours:
- Carcinoid tumours/carcinoid syndrome:
Circulating tumour markers for carcinoid tumours include chromogranin A, serotonin and tachykinins (e.g., substance P and neuropeptide A). Other markers include adrenocorticotropic hormone (ACTH), corticotropin releasing factor (CRF) and growth hormone-releasing hormone (GHRH), which are mostly associated with tumours of the foregut.
Significantly elevated levels of serotonin or its metabolites, especially increased urinary excretion of 5-hydroxyindoleacetic acid (5-HIAA), are observed in patients with carcinoid syndrome. Measurement of 5-HIAA is the most commonly used diagnostic test for this syndrome, with a sensitivity of 73% and a specificity of 100%. Elevated levels of substance P and chromogranin A also may be observed.
Flush provocation is the stimulatory test used for diagnosis;
it is done through pentagastrin stimulation or alcohol ingestion.
The amount of neuropeptide K is measured every 5 minutes for
30 minutes. CT, MRI, ultrasonography, and somatostatin receptor
scintigraphy may be used for tumour localisation.
Octreoscan (somatostatin receptor scintigraphy) of a patient with liver metastasis from a carcinoid tumour. The primary tumour located in the distal ileum also is present in the figure.
| Ultrasonography of liver metastases from a patient with carcinoid tumour. Ultrasound-guided biopsy can be taken during this procedure. |
Computerized tomography (CT) picture of liver metastases in a patient with an endocrine pancreatic tumour |
- Gastrinomas (Zollinger-Ellison syndrome):
A diagnosis is made based on the findings of an elevated serum gastrin level coupled with high basal acid output. The diagnosis may be further established by using secretin infusion testing to measure the level of gastrin every 5 minutes for 30 minutes. Chromogranin A is an excellent tumour marker as well.
Tumour localisation may be based on CT, MRI, ultrasonography, somatostatin receptor scintigraphy, and endoscopic ultrasonography. Antral and duodenal tumours, along with recurrent ulcer disease, may be observed using gastroscopy.
- Insulinomas (hypoglycaemic syndrome):
Serum insulin and pro-insulin are important tumour markers in
making a diagnosis, along with a fasting (48 to 72 hours) blood
glucose. A serum insulin-to-blood-glucose ratio of greater than
5.4 is indicative of insulinoma. Histopathology shows argyrophil
staining and synaptophysin immunohistochemistry. Imaging techniques
include CT with simultaneous angiography and endoscopic ultrasonography.
The latter procedure may reveal liver metastases.
- VIPomas (Verner-Morrison syndrome):
Diagnosis is based on elevated plasma levels of vasoactive intestinal peptide (VIP). The VIP molecule is very unstable, and careful preparation with protease inhibitors is essential. Histopathology shows argyrophil staining chromogranin A and VIP. Localisation of the tumour can be achieved using somatostatin receptor scintigraphy, CT angiography, MRI, or endoscopic ultrasonography.
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Testing methods
The following are available testing methods to diagnose and monitor GEP NE tumours. While the tests are effective, more accurate and simpler techniques still are needed.9
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