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 tumor development and proliferation. When a tumor occurs in the organism, certain tumor markers in the blood, cells, tissues or body fluids may be elevated accordingly. Through the examination of tumor markers, tumor patients can be detected at an early stage in the tumor census, which can help observe the efficacy of anti-tumor treatment and judge the prognosis. Currently, the main tumor markers found are: alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), glycogen 125 (CA 125), glycogen 153 (CA 153), glycogen 19-9 (CA 19-9), glycogen 724 (CA 724), glycogen 211 (CA 211), ferritin (Fer), neuron specific enolase (NSE), prostate specific antigen (PSA), and so on. specific antigen (PSA), tissue polypeptide antigen (TPA), glycogen 242 (CA242), human chorionic gonadotropin (HCG), β-human chorionic gonadotropin (β-HCG), sex and thyroid hormones, thyroglobulin (TG), antithyroglobulin (ATG), thyroid binding globulin (TBG), and antithyroid peroxidase (ATPO). Tumor markers have different manifestations in different tumors, e.g. CEA is often found in intestinal cancer and stomach cancer; CA199 is often found in intestinal cancer and pancreatic cancer; and CA153 is often found in breast cancer; so doctors will check different markers according to different tumors. However, the vast majority of tumor markers known today exist not only in malignant tumors, but also in benign tumors, embryonic tissues and even normal tissues. As a result, the specificity of tumor markers is relatively poor, which means that the rate of false positives and false negatives is high. Factors causing false positives include: 1. Some tumor marker expression may increase when certain benign diseases such as inflammation occur: for example, AFP, CA19-9, CEA, etc. may be elevated in viral hepatitis and cirrhosis of the liver; 2. Some physiological changes, such as pregnancy, may also elevate AFP, CA125, HCG; 3. CA19-9 may be elevated in rheumatic diseases. Similarly, tumor markers in the normal range can not completely exclude related tumors, such as the positive rate of AFP is only 75%~90%, that is to say, there are still about 10% of primary liver cancer patients with negative AFP. It can be seen that the diagnosis of tumor cannot rely on the examination of tumor markers alone, and the significance of single tumor marker elevation is not great, only the dynamic and continuous elevation has significance. If physical examination reveals that a certain tumor marker or several tumor markers are persistently elevated, then vigilance should be raised, and further CT, ultrasound and other methods of examination are needed; in particular, a clear diagnosis can only be made through pathological examination. If there is only a single mild elevation or no major change in the results of each examination, there is no need to be so nervous. In addition, for patients with malignant tumors, there is no absolutely specific tumor marker for any kind of malignant tumor, and each patient has their own base level for various tumor markers. Therefore, for different diseases and different patients can have different tumor markers as indicators for their efficacy monitoring. When the tumor improves after treatment or deteriorates due to tumor recurrence and metastasis, the changes in the levels of these tumor markers can be used as a reference. To sum up, various tumor markers can only be used as one of the indicators for auxiliary diagnosis. Before clear pathological and histological diagnosis is made, one should never be sure that he/she is suffering from cancer because of seeing a mild elevation of a certain indicator, or even carry out anti-tumor treatment, in order to avoid unnecessary harm and loss, but should be more vigilant for further examination and observation. If tumor marker is found to be relatively high in physical examination, it is recommended to insist on doing blood test once a month within six months to observe whether the indicator is persistently elevated or not, and if it is persistently elevated, it is necessary to do whole body imaging examination at once; if there are both high and low indicators of tumor marker in blood test, it is recommended to do a whole body physical examination in three to six months. The tumor markers that are worth paying attention to in general people’s physical examination are AFP, CEA, CA199, CA125, serum ferritin, which basically cover the common tumors.