A decrease in carcinoembryonic antigen to normal in lung adenocarcinoma indicates that anticancer treatment is effective and that the current treatment regimen can be continued. It indicates that the cancer cells are not active at this time, but it does not mean that it is cured. Carcinoembryonic antigen is an important indicator of lung adenocarcinoma. A decrease in the value of carcinoembryonic antigen indicates that the lung adenocarcinoma is under effective control and the tumor cells are more sensitive to the current treatment. If the carcinoembryonic antigen value rises again after a period of time, further examination is needed to confirm whether the tumor has recurred or metastasized. However, carcinoembryonic antigen is only an auxiliary indicator, whether the treatment is effective or whether there is recurrence or metastasis, further laboratory tests and imaging tests are needed to clarify. It is recommended that patients should have regular checkups, keep a good attitude and take active treatment to get a better prognosis.