We showed that the combination of flavopiridol (multi-CDK inhibitor) and carfilzomib (proteasome inhibitor) was synergistically effective in vitro using NCI-H295R, SW13, and BD140A ACC cell lines, and in vivo using NCI-H295R human ACC xenografts via the reduction of XIAP (anti-apoptotic protein) (39). Here, XIAP is linked to adrenal cortex carcinoma.