The use of CDK4/6i (abemaciclib, palbociclib, and ribociclib) plus ET as first-line therapy is considered the standard of therapy in patients with metastatic BC due to clinically meaningful benefits in terms of progression-free survival (PFS) [4,6], OS [8], time-to-chemotherapy [9], and quality of life [9]. Here, CDK4 is linked to breast cancer.