CEA is a glycoprotein that is often elevated in certain types of cancer, especially colorectal cancer. It is used as a tumor marker to help monitor cancer treatment, detect recurrence, and assess prognosis. Elevated levels of CEA can also be seen in other cancers, such as lung, pancreatic, and breast cancer, as well as in non-cancerous conditions like liver disease, inflammatory bowel disease, and chronic smoking. The test is commonly used in conjunction with other diagnostic methods.