BCL2 and Thrombocytopenia: Because BCL-XL controls platelet lifespan,74 ABT-737 and navitoclax provoke acute dose-limiting thrombocytopaenia.75, 76 Efforts to circumvent this problem led to the development of the BCL-2-specific venetoclax (ABT-199)73 that spares platelets.73, 77 Venetoclax differs from navitoclax primarily by engaging the p4 pocket in a manner that exploits a difference between BCL-2 (Asp103) and BCL-XL (Glu96).73