BIRC2 and neoplasm: Combinatorial loss of cIAP1 and cIAP2 in the endothelium (ciap1VECciap2−/− mice) displayed a similar reduction in tumor load compared to ciap1VECciap2frt/frt mice, suggesting cIAP1 alone is responsible for obstructing tumor cell extravasation past the endothelium barrier (Figure 4D).