A protein found inside neuroendocrine cells, which release CgA and certain hormones into the blood. CgA may be found in higher than normal amounts in patients with certain neuroendocrine tumors, small cell lung cancer, prostate cancer, and other conditions. Measuring the amount of CgA in the blood may help to diagnose cancer or other conditions or find out how well treatment is working or if cancer has come back. CgA is a type of tumor marker. Also called chromogranin A.