Pathology once immunohistochemistry means that it is impossible to determine the nature of the lesion, unable to determine the source of metastatic tumors, suspect the existence of tiny metastatic foci, etc. Immunohistochemistry can diagnose malignant tumors, pathologically typing malignant tumors, and determining metastatic foci. 1. Diagnose malignant tumor: Pathological examination is mainly carried out to determine the benign or malignant nature of the tumor through pathological examination of certain diseased tissues in the patient’s body. If it is a more complicated tumor, which cannot be detected by pathological examination, the benign or malignant nature of the tumor can be determined by immunohistochemistry. 2. Pathological typing of malignant tumors: for patients with malignant tumors confirmed by pathology, further pathological histochemical tests need to be done to clarify the progression of the tumors and to determine the typing of the tumors. 3. Determine the metastatic foci: if the malignant tumor has already metastasized, through the examination of immunohistochemistry, the metastatic site can be determined, which can provide the basis for the formulation of clinical treatment plan. Therefore, tumor patients should go to the hospital as soon as possible to clarify the cause of the disease, and actively cooperate with doctors for treatment after diagnosis.