A total of 19 patients (22.62%) with advanced breast cancer who received CDK4/6 inhibitors (n=84, ribociclib=47, palbociclib=32, abemaciclib=5) and 3 patients (18.75%) who received an mTOR inhibitor (n=16) were reported to have a PIK3CA mutation. Here, CDK4 is linked to breast cancer.