Enzymatic labeling, known as immunoenzymatic labeling (immunohistochemistry), can play a role in defining the type of tumor, in addition to other important roles, such as defining the site of the primary focus, further typing, assessing the prognosis, and guiding treatment. The basic principle of enzyme labeling, that is, the antigen-antibody reaction, i.e., the principle that antigen and antibody can bind specifically to identify antigens (peptides and proteins) in tissue cells and study them locally, qualitatively, and quantitatively relative to each other, is a commonly used technique in pathology examination. The main functions of immunohistochemistry are briefly described in the following aspects: 1. to determine whether the pathological section is malignant tumor. 2. to localize the site of the primary focus of a metastatic malignant tumor. 3. to typify definitive tumors. 4. can initially judge the prognosis of the tumor by some of these indicators, commonly used indicators such as Ki67. 5. It can play a guiding role in the treatment plan of malignant tumors, such as chemotherapy, molecular targeting therapy and other treatments. In conclusion, enzyme markers are very important in the pathological diagnosis of tumors. The significance of specific indexes and the decision of treatment program should follow the guidance of clinicians.