Ribociclib (7-cyclopentyl-N,N-dimethyl-2-[(5-piperazin-1-ylpyridin-2-yl)amino]pyrrolo[2,3-d]pyrimidine-6-carboxamide) is also an FDA-approved CDK4/CDK6 inhibitor combined with a fulvestrant or aromatase inhibitor for ER-positive/HER2-negative advanced breast cancer treatment in postmenopausal women [84,101]. This evidence concerns the gene ESR1 and breast cancer.