The carcinoembryonic antigen (CEA) test is used to find how widespread cancer is for some types of the disease, especially colon cancer. It is also used to check the success of treatment for colon cancer. CEA levels may be measured both before and after surgery to evaluate both the success of the surgery and the person's chances of recovery and during treatment with chemotherapy. This provides information about how well the treatment is working and to moitor whether the cancer has returned after treatment.