CD33 also known as SIGLEC3, p67 is a type I transmembrane glycoprotein primarily located on the surface of granulocyte and macrophage precursors in the bone marrow, while being absent from pluripotent stem cells. Expression on monocytes in peripheral blood makes CD33 a crucial marker for distinguishing myelogenous leukemia cells from lymphoid or erythroid leukemias. CD33 may function as a sialic acid-dependent cell adhesion molecule, which is important for mediating interactions between immune cells and their environment, thereby influencing immune responses and cell signaling pathways. Understanding CD33′s role in these processes can provide insights into potential therapeutic targets in various hematological malignancies.