Tumor markers are a class of substances that are synthesized or released by tumor cells or produced by the body in response to tumor cells during the process of tumorigenesis and proliferation. When tumor occurs in the body, certain tumor markers in blood, cells, tissues or body fluids may increase accordingly. Tumor markers can be used to detect tumor patients at an early stage in tumor screening, to help observe the efficacy of anti-tumor treatment and to judge the prognosis. The main tumor markers found so far are: alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), glycogen 125 (CA125), glycogen 153 (CA153), glycogen 19-9 (CA19-9), glycogen 724 (CA724), glycogen 211 (CA211), ferritin (Fer), neuron-specific enolase (NSE), prostate specific antigen (PSA), tissue polypeptide antigen (TPA), glycogen 242 (CA242), human chorionic gonadotropin (HCG), beta-human chorionic gonadotropin (beta-HCG), sex and thyroid hormones, thyroglobulin (TG), antithyroglobulin (ATG), and thyroid binding globulin (TBG), anti-thyroid peroxidase (ATPO). The significance of the reference range of tumor markers Tumor markers have different manifestations in different tumors, for example, CEA is often found in intestinal cancer and gastric cancer; CA199 is often found in intestinal cancer and pancreatic cancer; CA153 is often found in breast cancer; so doctors will check different markers according to different tumors. However, most of the tumor markers known today exist not only in malignant tumors, but also in benign tumors, embryonic tissues, and even normal tissues. Therefore, the specificity of tumor markers is relatively poor, which means that the rate of false positives and false negatives is relatively high. Factors that cause false positives include: 1. When some benign diseases such as inflammation occur, the expression of some tumor markers may increase: for example, AFP, CA19-9 and CEA may be elevated in viral hepatitis and liver cirrhosis; 2. Some physiological changes such as pregnancy, AFP, CA125 and HCG may also be elevated; 3. CA19-9 may be increased in rheumatic diseases. Similarly, tumor markers within the normal range cannot completely exclude related tumors, for example, the positive rate of AFP only reaches 75%-90%, which means that about 10% of primary liver cancer patients have negative AFP. Thus, the diagnosis of tumor cannot rely on tumor marker examination alone, and the significance of single elevation of tumor marker is not significant, but only the dynamic and continuous elevation is meaningful. If physical examination reveals a certain or several tumor markers are persistently elevated, then vigilance should be raised and further CT, ultrasound and other methods of examination are needed; especially pathological examination is required for clear diagnosis. If there is only a single mild elevation or no big change in the result of each examination, it is not necessary to be so nervous. In addition, for malignant tumor patients, there is no absolute specific tumor marker for any kind of malignant tumor, and each patient has their own base level for various tumor markers. Therefore, there are different tumor markers for different diseases and different patients as their efficacy monitoring indicators. When the tumor improves with treatment or deteriorates due to tumor recurrence and metastasis, the changes of these tumor markers levels can be used as a reference. In conclusion, various tumor markers can only be used as one of the auxiliary diagnostic indicators. Before a clear pathological histological diagnosis is made, one should never be sure that one has cancer or even carry out anti-tumor treatment just because one sees a mildly elevated indicator to avoid unnecessary harm and loss, but should be vigilant for further examination and observation.