Chromogranin A (CgA) is an 86 kDa protein that is the major member of the granin family of acidic secretory glycoproteins located in neurosecretory granules of neuroendocrine cells. Chromogranin A showed broad expression in endocrine tissues including pituitary, adrenal medulla, thyroid, pancreatic islets and gastrointestinal tract. Chromogranin A represents the single most specific marker of neuroendocrine differentiation in general use. It is useful for identification of neuroendocrine tumors.