Though it is a promising target, many CDK9 inhibitors lack specificity and also target other CDKs, resulting in significant off-target effects and toxicity.103 Some of the first P-TEFb/CDK9 inhibitors, BAY 1143572 (atuveciclib) and BAY 1251152, were entered into clinical trials for advanced hematologic malignancies but failed to establish safety or efficacy to move to phase II clinical trials (NCT02345382, NCT02745743). The gene discussed is CDK9; the disease is hematologic disorder.