Despite these progresses, cytotoxic chemotherapy (ChT) remains a mainstay for the treatment of almost all patients with HER2-negative mBC: in TNBC, single-agent or combination ChT are the only available therapeutic options for the vast majority of patients in all treatment lines; in HR+ HER2- BC with primary or acquired resistance to endocrine therapies, ChT is the only effective treatment to control disease growth, to relieve patient symptoms and to prolong survival [1]. This evidence concerns the gene ERBB2 and breast cancer.