Immunohistochemistry is a means of pathological examination and is generally more commonly used in routine pathological diagnosis of tumors, especially for the differential diagnosis of poorly differentiated or undifferentiated tumors with a high accuracy. Immunohistochemistry may assist in the diagnosis of suspected malignant tumors to be confirmed, or when it is difficult to determine the pathological staging, immunohistochemistry can help to determine. The principle of immunohistochemical examination is mainly the antigen-antibody reaction of immunology, which can detect the presence of specific antigens in the corresponding tissue cells by labeled antibodies, and quantitative and localized detection of specific antigens, which is usually highly targeted and sensitive. Specific tumors have specific immunohistochemical counterparts. For example, for some mesenchymal tumors, it can reflect the degree of tumor proliferation, and the higher the index, the stronger the ability to proliferate malignantly. For neuroendocrine tumors, immunohistochemical results can be used as criteria for tumor grading. Immunohistochemical examination for breast cancer can determine the treatment modality of patients.