NOTCH1 and breast cancer: Further, Notch-1 transcriptional activity was suppressed by overexpression of (EGFR)-2 (ErbB-2 or HER2/neu) protein (ErbB-2) in breast cancer cells, and inhibition of ErbB-2 using trastuzumab reactivated Notch-1 activity which might explain the low efficacy of trastuzumab in sensitive cells or the development of resistance [81].