Additionally, since one of the possible failures of the clinical trials conducted so far with TRAs is the lack of (a) suitable biomarker(s) for patient stratification, identifying patients more – or less – likely to respond to a TRA-comprising therapy, and since CDK9 was found to be highly expressed in cancer tissue compared to the healthy counterpart [133], high CDK9 expression could be considered as an inclusion criterion for therapies that comprise the combination of effective TRAs with drugs capable of inhibiting CDK9. This evidence concerns the gene CDK9 and cancer.