الفهرس 
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Abstract
The measurement of general and specific markers offers important information for the clinician treating patients with gastrointestinal neuroendocrine tumors. Not only does this information assist with the initial diagnosis but it also offers an easy means of monitoring patients who have inactive disease or who are undergoing treatment.
CgA is the most useful circulating marker for neuroendocrine tumors of the gastrointestinal tract. It does not only reflect the metabolic activity of the tumor but also generally correlates with tumor burden. It is also a useful marker for monitoring patients during treatment with the limitation that its serum level may decline due to the suppressive effect of somatostatin analogues without corresponding reduction in tumor mass .
Measurements of 24 hour urinary 5-HIAA together with plasma CgA should be done together in patients with clinical carcinoid syndrome of both foregut and mid-gut type. Two 24-hour urine collections are recommended following appropriate restriction of food and medication.
Other general neuroendocrine tumor markers such as NSE, PP and CgB have much lower sensitivity and specificity than CgA, and consequently are not recommended for routine investigations.
In addition to general neuroendocrine tumor markers, there are specific peptides which are released into the circulation from specific tumors and reliable assays are available for the measurement of these cell products. The measurement of these specific peptides is important to monitor tumor activity, progression of disease, response to treatment, recurrence and change in cell type associated with worsening of prognosis.