ACVR2B, also known as Activin A Receptor Type IIB or ActR-IIB, is a transmembrane serine/threonine kinase receptor encoded by the ACVR2B gene. It belongs to the Transforming Growth Factor-β (TGF-β) superfamily and plays a crucial role in various biological processes. ACVR2B is expressed in multiple tissues, with high levels in tumor cells. It binds to Activin A, recruiting and phosphorylating type I activin receptors, and subsequently signals through SMAD2/3 proteins to regulate cell proliferation, differentiation, and migration. Mutations in ACVR2B have been associated with left-right axis malformations and heterotaxy syndrome.