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.

It is an excellent marker for carcinoid tumors, pheochromocytomas, paragangliomas, and other neuroendocrine tumors. Co-expression of chromogranin A and neuron specific enolase (NSE) is common in neuroendocrine neoplasms. Reportedly, co-expression of certain keratins and chromogranin indicates neuroendocrine lineage. The presence of strong anti-chromogranin staining and absence of anti-keratin staining should raise the possibility of paraganglioma. The co-expression of chromogranin and NSE is typical of neuroendocrine neoplasms. Most pituitary adenomas and prolactinomas readily express chromogranin.