Chromogranin A (CGA) is a soluble acidic protein with the highest content in human adrenal medulla. It is widely expressed in neurons, neuroendocrine cells and tumor cells. It is mainly used in the judging of neuroendocrine tumors such as pituitary tumors, islet cell tumors, pheochromocytomas, medullary thyroid tumors, carcinoid tumors, etc.