Tumor markers, also known as tumor markers, are chemical substances that characteristically exist in malignant tumor cells, or are produced abnormally by malignant tumor cells, or are produced by the host in response to tumor stimulation and reflect the presence of tumors, and can reflect tumor occurrence and development and monitor tumor response to treatment. Tumor markers are either not found in normal adult tissues but only in embryonic tissues, or are present in tissues, body fluids and excreta of tumor patients at levels much higher than those in normal tissues, and can be detected by immunological, biological and chemical methods. Their presence or quantitative changes can suggest the nature of the tumor and lend to the understanding of tumor histogenesis, cell differentiation, and cell function to help in tumor diagnosis, classification, prognosis judgment, and treatment guidance. The main categories are as follows: 1. oncofetalproteins, such as methemoglobin and carcinoembryonic antigen; 2. tumor-associatedantigens, such as CA19-9 and CA125; 3. enzymes, such as lactate dehydrogenase, neuron-specific enolase, prostate acid phosphatase; 4. In addition, proto-oncogenes, oncogenes and their products are increasingly used as tumor markers.