Lymphocytic infiltration is actually the presence of a large number of lymphocytes within or around a lesion. This lymphocytic infiltrate can be present in tumor lesions or in inflammatory tissue. It also depends specifically on the patient’s main symptoms to determine whether it is an inflammatory or tumor cell infiltrate. Lymphocytes, a type of white blood cell, are the smallest white blood cells produced by lymphoid organs and are an important cellular component of the body’s immune response function. If there is an obvious inflammatory lesion in the patient, lymphocyte infiltration is the presence of lymphocytes at the site of inflammation since lymphocytes belong to the leukocyte system. If a tumor is present in the patient, lymphocyte infiltration refers mainly to the presence of lymphocytes in large numbers around the tumor, where the lymphocytes are activated to recognize and kill the tumor cells.