ERBB2 and breast cancer: Triple-negative breast cancer (TNBC), a phenotypic subtype of BC that is defined as negative for hormone receptors and human epidermal growth factor receptor 2 (HER2), accounts for approximately 10–20% of all BC patients and is a highly aggressive disease with a poor diagnosis and outcomes (the 5-year survival rate is less than 30% for patients with advanced TNBC) [2–4].