To date, few studies investigate targeted approaches for AI-resistant breast cancer such as the use of lapatinib [5,11], intermittent letrozole treatment [12,13], histone deacetylase (HDAC) inhibitors [12,14], cdk4/6 inhibitors [15], or co-targeting cdk2 and cdk4/6 [16]. Here, CDK4 is linked to breast cancer.