It was found that CDK4/CDK6 inhibitors can be combined with a variety of drug treatment models that have been investigated in preclinical models of various tumor types, and many of which are presently undergoing clinical trials (http://www.clinicaltrials.gov), which include palbociclib and letrozole in HR+/HER2‐negative operable breast cancer, palbociclib in combination with tamoxifen as the first line therapy for metastatic hormone receptor positive breast cancer, palbociclib with fulvestrant for metastatic breast cancer, and palbociclib and cetuximab in metastatic colorectal cancer. This evidence concerns the gene CDK4 and breast cancer.