Tumor markers refer to a class of substances that are biosynthesized, released by tumor cells or are host-responsive to cancer types during tumorigenesis and proliferation. These substances may be circulating substances that can occur in cells, tissues or body fluids and can be detected qualitatively or quantitatively in blood or secretions using chemical, immunological and molecular biology techniques. The analysis of the properties of such substances is used as a marker to identify tumor cells. Characteristics that a tumor marker should have: it must be produced by malignant tumor cells and measurable in blood, tissue fluid, secretion or tumor tissue; it should not be present in normal tissues and benign diseases; the tumor marker of a particular tumor should be detected in the majority of patients with that tumor. The tumor marker should be detectable before there is clear clinical evidence of tumor; the amount of tumor marker should reflect the size of the tumor; it can help to estimate the effect of treatment and predict the recurrence and metastasis of tumor to some extent. Most of the known tumor markers exist not only in malignant tumors, but also in benign tumors, embryonic tissues, and even normal tissues. Therefore, these tumor markers are not specific products of malignant tumors, but they are significantly increased in patients with malignant tumors, so they are also called tumor-associated antigens. To detect tumor markers, except for some serum enzymes that can be quantified by measuring viability, most of the proteins or other tumor markers without enzyme viability need to be determined by immunological methods. The physical examination report mainly compares the tumor marker detection value with the normal reference value. If there is a very obvious increase, the cancer suspicion is very high and further comprehensive examination should be done, and if necessary, a PET-CT whole body scan is needed. Even if the level is slightly over the standard, it should not be ignored. In order to completely exclude the possibility of early stage of cancer, it is necessary to go to the hospital for rechecking every one or two months. If the elevation persists, cancer is suspected to be developing. If there is no significant elevation all the time, it is usually a benign lesion, which may be an organ inflammation. If a cancer patient finds that the marker is significantly higher after surgery than before surgery, the possibility of recurrence should be considered and further examination should be requested from the doctor in time to determine whether it is a recurrence.