According to the results of the PALOMA [9–11], MONARCH [12, 13], and MONALEESA [14–16] studies published in recent years, the use of cyclin-dependent kinase 4 and 6 inhibitors (CDK 4/6i) plus ET has become the first-line standard treatment in most patients with HR-positive, HER2-negative BC [17]. Here, ERBB2 is linked to breast cancer.