ERBB2 and breast cancer: However, we also found that breast cancer cell lines with lower EGFR and HER2 expression (ZR-75-1 and MCF-7) showed low IC50, from 1.81 μM to 2.99 μM. These results indicate that 5a not only targets EGFR and HER2 but may also target other gene(s) and/or protein(s) in breast cancer cells.