XIAP and acute myeloid leukemia: Currently, the expression of Bcl-2, MDM2 and XIAP seems to be the biomarker of choice for Bcl-2 inhibitors, MDM2 antagonists and XIAP inhibitors/SMAC-mimetics, but the expression of these proteins may vary at different stages of the disease (primary diagnosis vs relapse vs refractory setting) and how this correlates with the various subclasses of AML is still currently under investigation.