Chromogranin is a protein made by some neuroendocrine tumours including carcinoid. It is also made by some other types of cancer, such as small cell lung cancer and neuroblastoma. A higher than normal level of CgA in the blood is a marker for these tumours. Doctors use CgA to diagnose and monitor the effects of treatment in people with tumours of the neuroendocrine system and some prostate cancers.