XIAP and cancer: The expression of DRs and proapoptotic (Bid, Bax, Bak, Smac/DIABLO) or antiapoptotic (FLIP, Bcl-2, Bcl-xL, Mcl-1, Akt, IAP-1, IAP-2, XIAP, survivin) proteins in cancer cells is involved in TRAIL-resistance [4, 5, 41, 49, 50].