Immunohistochemistry is a frequently performed test in pathology department, and its main function is to diagnose and differential diagnosis of tumors, as well as to classify tumors in a more detailed way. After immunohistochemistry is added, especially for some poorly differentiated or undifferentiated tumors, its diagnostic accuracy can reach 50%-75%. Specifically, the main roles of immunohistochemistry in clinical practice include many aspects, such as diagnosis and differential diagnosis of malignant tumors, determination of the primary site of metastatic malignant tumors, and further pathological classification of certain tumors, etc. Therefore, immunohistochemistry can assist pathology departments to better diagnose and differentially diagnose tumors and provide clinical options for treatment.