ERBB2 and breast cancer: The introduction of cyclin-dependent kinase 4 and 6 inhibitors (CDK 4/6i) in combination with endocrine therapy for the treatment of women with hormone receptor-positive (HR)/human epidermal growth factor receptor 2-negative (HER2) breast cancer has radically changed the treatment of patients with breast cancer, improving their health-related quality of life and life expectancy, with a high response rate and longer median progression-free survival (PFS) and overall survival (OS) [1,2,3,4,5,6,7,8].