XIAP and acute myeloid leukemia: However, many primary tumors, including AML, are resistant to the pro-apoptotic effects of recombinant human TRAIL (rhTRAIL) through a variety of mechanisms including reduced expression of DR4/DR5, elevated expression of TRAIL decoy receptors [8] and increased expression of anti-apoptotic proteins such as cellular-FLICE-inhibitory protein (c-FLIP) and X-linked inhibitor of apoptosis protein (XIAP) [9-11].