BIRC6 is a large anti-apoptotic protein belonging to the inhibitor of apoptosis (IAP) family that uniquely functions as a dual E2/E3 ubiquitin ligase, combining ubiquitin conjugating and ligase activities in a single polypeptide 1. Unlike other IAPs, BIRC6 lacks a RING domain and instead works exclusively with the noncanonical E1 ubiquitin activating enzyme UBA6 1. The protein directly inhibits executioner caspases-3 and -7 and ubiquitinates caspases-3, -7, and -9, thereby preventing apoptosis 1. BIRC6 also ubiquitinates pro-apoptotic factors DIABLO/SMAC and HTRA2, though SMAC can antagonize BIRC6's function through competitive binding 1. Beyond apoptosis regulation, BIRC6 participates in a ubiquitination cascade with UBA6, KCMF1, and UBR4 that regulates the integrated stress response in aneuploid epithelial tumors 2. Clinically, BIRC6 overexpression correlates with poor prognosis in multiple cancers, including epithelial ovarian cancer where it predicts tumor recurrence and reduced survival 3, and childhood acute leukemia where higher expression associates with unfavorable therapeutic response and shorter survival 4. These findings highlight BIRC6 as both a critical cellular survival regulator and potential therapeutic target.