ERBB2 and breast cancer: Nearly 60% of female patients with breast cancer aged under 50 are hormone receptor (HR)- positive and human epidermal growth factor receptor 2(HER)-negative (4), while the contemporary standard of care treatment in pre- and post-menopausal patients comprises endocrine therapy with the addition of everolimus or cyclin dependent kinases (CDK) 4 and 6 inhibitors (5–7).