Carcinoembryonic antigen may be elevated after immunotherapy for lung adenocarcinoma. Carcinoembryonic antigen is a broad-spectrum tumor marker, and elevated carcinoembryonic antigen is commonly seen in gastrointestinal tumor diseases, and some patients with lung adenocarcinoma may have elevated carcinoembryonic antigen. Elevated carcinoembryonic antigen after immunosuppressive therapy may be seen in lung adenocarcinoma that is not well treated with immunotherapy, or in patients with other tumors of the digestive system, breast cancer, and other oncological diseases. Elevated carcinoembryonic antigen is not only seen in oncologic diseases, but also in smoking, pregnancy, pancreatitis, diabetes mellitus, cardiovascular diseases and other conditions. Therefore, patients with elevated carcinoembryonic antigen after immunotherapy for lung adenocarcinoma should go to the hospital in time to improve the examination and give targeted treatment after clarifying the cause of the disease, so as to avoid further development of the disease.