Carcinoembryonic antigen (CEA) is a glycoprotein first identified by Gold and Freedman in 1965 from fetal and colon cancer tissues. In general, CEA is synthesized by cells in the epithelial tissue of the fetal gastrointestinal tract, pancreas, and liver, and is usually elevated during the first 6 months of pregnancy. Therefore, for the health and well-being of the smoker and the whole family, it is recommended to quit smoking as soon as possible. CEA is a non-specific tumor-associated antigen, and most of the tumors that secrete CEA are located in the gastrointestinal tract, respiratory tract, urinary tract, and breast. Under normal conditions, CEA is metabolized by the gastrointestinal tract, while CEA in the tumor state enters the blood and lymphatic circulation, causing an abnormal increase in serum CEA, so that the serum CEA levels of patients with various tumors mentioned above are increased. In clinical practice, when CEA is greater than 20μg/L, it is seen in colon cancer, rectal cancer, gastric cancer, lung cancer and so on. However, abnormally elevated CEA is rarely seen in primary liver cancer. If the examination reveals that there is also cystic dark area in the liver which may be liver cyst, liver MRI can be done to make a clear diagnosis, and if the diagnosis is still not clear, liver puncture biopsy is necessary. Liver cyst is a benign lesion, and since the cyst is small (less than 1 cm), it will not affect liver function and no therapeutic measures are necessary, and can be followed up with regular checkups.