ERBB2 and breast cancer: TNBC is further subclassified as basal-like breast cancer (BLBC, ER-/PR-/HER2-/CK5/6+or epidermal growth factor receptor [EGFR] +) and quintuple-negative breast cancer (QNBC, ER-/PR-/HER2-/CK5/6-/EGFR-) and accounts for 15–25% of all breast cancer cases [3].