There are various reasons why carcinoembryonic antigen is still high even after taking targeted drugs, mainly due to two major reasons: tumor drug resistance and tumor metastasis. In addition, inflammation and other benign factors may also cause elevated carcinoembryonic antigen. 1. Tumor drug resistance: Targeted drugs are used to inhibit the specific gene target of tumor cells, which may lead to the disappearance of drug effect due to the occurrence of target drug resistance in the process of taking drugs. At this time, genetic testing can be repeated to select new therapeutic targets or other anti-tumor treatments. 2. Tumor metastasis: At the same time, recurrence and distant metastasis may occur in the course of treatment due to the high degree of malignancy of the tumor, which may lead to the elevation of carcinoembryonic antigen. At this time, the patient’s condition can be reassessed to decide whether to maintain the original medication or switch to other treatment options. There are also many other reasons for elevated carcinoembryonic antigen, such as inflammation and other benign factors that can lead to elevated carcinoembryonic antigen. However, patients with malignant tumors need to be vigilant about the progression of their disease and are advised to go to the hospital for a comprehensive examination, which requires imaging and other tests to assess whether their disease has changed, and cannot be based on elevated carcinoembryonic antigen alone.