CDK9 and breast carcinoma: Lastly, the inhibition of CDK9 activity, in the resistant cell lines, with the small-molecule inhibitor CAN-508, showed a dose-dependent inhibition of cell growth, in conjunction with ~60% reduction in cMYC mRNA and proteins, highlighting the critical role of CDK9 in the up-regulation of cMYC expression in endocrine therapy-resistant ERα+ breast cancer patients [89].