CD61, also known as integrin β3 or GPIIIa, is a membrane glycoprotein primarily expressed on platelets, megakaryocytes, endothelial cells, osteoclasts, and some tumor cells. It forms heterodimeric complexes with other integrins, such as CD41 (forming the GPIIb/IIIa complex) or CD51 (forming the αvβ3 integrin), which mediate cell adhesion to various extracellular matrix proteins, including fibrinogen, fibronectin, and vitronectin. The GPIIb/IIIa complex is essential for platelet aggregation and blood clotting, while the αvβ3 integrin is involved in cell migration, invasion, and tumor metastasis. In clinical settings, CD61 is used as a biomarker to identify platelets and megakaryocytes, diagnose platelet disorders like Glanzmann thrombasthenia, and assess the risk of thrombotic events. Additionally, elevated CD61 expression in tumors is associated with poor prognosis in several cancers, including non-small cell lung cancer, breast cancer, and gliomas.