Immunohistochemistry, short for immunohistochemistry, is the application of the basic principles of immunology, that is, the antigen-antibody reaction, i.e., the principle that antigens and antibodies can bind specifically, to identify antigens (peptides, proteins) in tissue cells and to study their localization, characterization, and relative quantification. Therefore, it is called immunohistochemistry technique, or immunohistochemistry for short, and is a common technique for pathology examination. The basic principle is to use the principle that there is a highly specific binding between antibodies and antigens in the human body. It mainly includes the following classified techniques: 1. immunofluorescence cytochemistry; 2. immunoenzymatic cytochemistry; 3. immunocolloid gold technique. Its application in clinical practice mainly includes the following aspects: First, diagnosis and differential diagnosis of malignant tumors. Second, to determine the primary site of metastatic malignant tumors. Third, further pathological typing and histological classification of certain tumors to detect micro metastases and provide some basis for clinical formulation of treatment plans.