ERBB2 and breast cancer: However, within a panel of ERBB2+ breast cancer cell lines (Fig. 1a, Additional file 2: Figure S1A), trastuzumab only efficiently inhibited the growth of the high ERBB2-expressing ZR-75-30 cell line (Fig. 1b, IC50 0.2 μg/mL, ~ 1.3 nM).