| Summary: | As there are many different subtypes of neuroendocrine tumors (NETs), many kinds of markers are used for their diagnosis and follow-up. Most of these markers, such as calcitonin, catecholamines, 5-hydroxyindoleacetic acid (5-HIAA), insulin, gastrin, pancreatic polypeptide, and glucagon are specific to one subtype of NET. In addition, there are also general markers used in various NET subtypes; the most commonly used ones are chromogranin-A (CgA), neuron-specific enolase (NSE), and synaptophysin. The sensitivity and specificity levels of CgA are highest among all NET markers. However, specific markers, such as calcitonin in medullary thyroid carcinoma, insulin in insulinoma and cathecolamines in feocromocitoma are more useful than CgA. CgA is an auxiliary marker in cases with relapse or metastasis of such functional NETs. Carcinoid syndrome is characterized by serotonin hypersecretion with the other products and 5-HIAA level is used to determine the serotonin hypersecretion. Thus, 5-HIAA is the specific marker for carcinoid tumors which comprise two-thirds of all NETs.
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