Currently, the CDK9 inhibitor flavopiridol is being evaluated in several phase I and II clinical trials for its anti-cancer effects either as a single agent or in combination with other drugs in treatment of esophageal cancer, B-cell chronic lymphocytic leukemia, endometrial carcinoma, recurrent/metastatic squamous cell carcinoma and most relevantly, previously treated locally advanced or metastatic breast cancer (http://www.cancernetwork.com/review-article/current-clinical-trials-flavopiridol/page/0/2). Here, CDK9 is linked to metastatic squamous cell carcinoma.