Tumor markers, also known as tumor markers, are substances characteristically present in malignant tumor cells, or produced abnormally by malignant tumor cells, or produced by the host in response to tumor stimulation, and can reflect tumor occurrence and development and monitor tumor response to therapy. Tumor markers are found in the tissues, body fluids and excretions of tumor patients and can be detected by immunological, biological and chemical methods. Sources of tumor markers The sources of tumor markers are divided into four main categories, namely metabolites of tumor cells, gene products of cells with disordered differentiation, substances released into the blood circulation by necrotic disintegration of tumor cells, and cellular reactive products of tumor host cells. 1. Metabolic products of tumor cells, such as glycolysis products, tissue peptide antigens, nucleic acid breakdown products. 2.Disordered differentiation cell gene products, such as: ectopic ACTH fragments, methemoglobin, carcinoembryonic antigen, fetal isoenzymes. 3.Materials released into the blood circulation by necrotic disintegration of tumor cells, mainly certain cytoskeletal protein components, such as cytokeratin fragment antigen 21-1 (Cyfra21-1), polyamines. 4. Cellular reactive products of tumor host cells, such as VCA-IgA and EA-IgA. 5 types of people can be screened for tumor markers 1. healthy people over 40 years old; 2. people with “cancer signals”; 3. people who work in seriously polluted factories and mines; 4. people with long-term exposure to carcinogenic substances; 5. people with high cancer incidence or family history of cancer. People in high incidence areas or those with family history of cancer. The sensitivity or specificity of individual markers is often low and cannot meet clinical requirements. In theory and practice, it is advocated that multiple markers should be measured at the same time to improve sensitivity and specificity; tumor markers are not the only basis for tumor diagnosis, but should be considered clinically in combination with other means such as clinical symptoms and imaging examinations. The diagnosis of tumor must be based on histopathology or cytopathology. Due to the individual differences of patients and their specific clinical conditions, the analysis of tumor markers should be combined with clinical conditions and compared from multiple perspectives in order to reach objective and realistic conclusions.