ERBB2 and breast cancer: Many phase III trials investigating CDK4/6i plus ET demonstrated an improvement in progression free survival (PFS) with mixed results in overall survival (OS) in advanced or metastatic HR+/HER2- BC [[6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]].