The danger of elevated tumor markers depends on the situation. If a patient is found to have elevated tumor markers, the first thing to do is to rule out the possibility of having a tumor, but there is no need to be overly concerned, as false-positive increases in tumor markers can occur in people with benign diseases, inflammation, and in smokers. If carcinoembryonic antigen is mildly elevated in smokers, regular checkups are sufficient; if it is more than 2-3 times higher than the normal value or still high after checkups, targeted examinations of the gastrointestinal tract and lungs are needed. If these tests are normal, close observation is needed until the carcinoembryonic antigen returns to normal in the short term.