Because many clinical trials are in place to test the possibility to treat luminal MBCs with drugs targeting kinases other than CDK4/CDK6 [1], we applied here our screening methods and administered a library of kinase inhibitors to ET drugs sensitive (i.e., MCF-7 cells) and resistant (i.e., Tam Res and Y537S MCF-7 cells) BC cell lines [14, 15] to identify kinase inhibitors working as ‘anti-estrogen-like’ drugs. This evidence concerns the gene CDK4 and breast cancer.