AR and Familial prostate cancer: However, a new selective CDK9 inhibitor, KB-0742 has been shown to display potent antitumor activity in prostate cancer models and to downregulate key androgen receptor–driven transcriptional pathways (23) while KB-0742 and the D11 CDK9 inhibitor have been reported to target MYC-high triple-negative breast cancers (24, 25).