Physicians are treating patients with estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer with an increasingly complex sequence of therapies using CDK4/6 inhibitors and antibody-drug conjugates. CDK4/6 inhibitors such as palbociclib, ribociclib, and abemaciclib are used in combination with hormone therapy to stop cell division in tumors[1][5]. These drugs, in combination with endocrine therapy, almost double the time to disease progression and delay the onset of endocrine resistance[1]. Treatment with CDK4/6 inhibitors with hormonal therapy produces a long-lasting response and significantly delays the need for chemotherapy, which improves the quality of life of patients[1]. All international professional societies recommend combined endocrine therapy with CDK4/6 inhibitors already in the first line of treatment for HR+/HER2- advanced or metastatic breast cancer[1]. Inhibition of CDK4/6 helps reverse or delay resistance to hormone therapy in patients with advanced breast cancer[2].