CD45 is transmembrane protein that is present on all differentiated hematopoietic cells (including basophils, granulocytes, lymphocytes, macrophages / histiocytes, mast cells, monocytes, dendritic cells, medullary thymocytes, plasma cells). Erythrocytes and their immediate progenitors do not express CD45 antigen. This antigen is used in routine immunohistochemistry to differentiate between immune cell types, as well as to differentiate hematological malignancies from other tumors. CD 45 is a good marker for AML, ALCL and most B- and T-cell lymphomas. Epithelial tumors, follicular dendritic cell sarcomas, germ cell tumors, melanoma, mesothelioma do not express CD45.