Immunohistochemistry is an option when trying to determine if certain proteins are expressed in a tissue. In most cases, immunohistochemistry should be performed to further characterize a rigorous pathological diagnosis. Specifically for tumors, immunohistochemistry can be performed to determine the benign or malignant nature of a tumor, to see if there is infiltration of the tumor, or lymphovascular or vascular invasion, or to determine the cellular properties of the tumor, or to determine the origin of the tumor. When classifying certain undifferentiated malignant tumors, for example, whether it is a sarcoma or lymphoma, and which subtype of the sarcoma or lymphoma. And when there are early metastases on lymph nodes, for example, but it is not too easy to distinguish them. In all of these scenarios, immunohistochemistry will be applied to determine whether there is a specific protein expression to make a classification judgment. In conclusion, a rigorous pathologic diagnosis will apply immunohistochemistry in most cases. Its purpose is to determine whether various meaningful proteins are expressed or not to increase the accuracy of the pathologic diagnosis.