CDK4 and breast cancer: Many other genomic alterations have been investigated in plasma ctDNA of patients treated with CDK4/6 inhibitors due to their role around the cyclin D-CDK4/6-Rb axis or in breast cancer in general, namely CCND1, CDK4, CDK6, CDKN1, CDKN2, NF1, ERBB2, AKT1, NRAS, HRAS, GATA3, and MYC[39,78,83].