ERBB2 and breast cancer: Their addition to traditional endocrine therapy, either in first-line or late-line setting has significantly improved the progression-free survival (PFS) and overall survival (OS) compared to endocrine therapy alone, in patients with metastatic ER-positive HER2-negative BC [40,41,42]; even so, their long-term efficiency seems to be also limited by the occurrence of drug resistance [43].