CASP9 and Thrombocytopenia: While the use of ABT-263 in patients is dose-limited due to causing thrombocytopenia via suppression of BCL-xL in platelets [93], loss of caspase-9 confers resistance to ABT-737, suppressing phosphatidylserine exposure and delaying APT-737-stimulated thrombocytopenia in vivo [94].