CD61, also known as integrin β3 or GPIIIa, is a membrane glycoprotein that forms heterodimeric complexes with other integrins, such as CD41 （forming the GPIIb/IIIa complex） and CD51 （forming the αvβ3 integrin）. It is primarily expressed on platelets, megakaryocytes, endothelial cells, osteoclasts, and some tumor cells. The CD61/CD41 complex is crucial for platelet aggregation and blood clotting through interactions with fibrinogen and von Willebrand factor. Additionally, CD61 plays a role in cell adhesion, migration, and invasion in various physiological and pathological processes, including tumor metastasis and viral infections. In clinical settings, CD61 is used as a biomarker for identifying platelets and megakaryocytes, and its upregulation in tumors is associated with poor prognosis in several cancers.