Cluster of differentiation 43 (CD43), also known as sialophorin, is a transmembrane protein that plays a role in T cell activation. CD43 is normally expressed abundantly on the surface of differentiated hematopoietic stem cells, including monocytes, granulocytes, T lymphocytes, and some B lymphocytes. Due to the efficacy of CD43 immunohistochemical staining in granulocytes, it is an effective marker for myeloid tumors, while other antibodies demonstrate weak staining under these conditions. Given the low reactivity of Anti-CD43 with B cells, positive staining of CD43 is implicated in a number of lymphoid and myeloid tumors, with over 90% positive staining in T-cell lymphomas. When CD43 is used in combination with CD45 and L26, immunotyping of various lymphomas can be obtained. This is particularly true when co-staining a lymphoid infiltrate with CD20 and CD3, thereby favoring lymphomas.