ERBB2 and breast carcinoma: Similarly, T-DM1 demonstrated an objective response rate (ORR) of 41.3% (95% confidence interval: 30.4% to 52.8%) in patients who had breast cancer with a marked overexpression of HER2, and T-DM1 showed much less antitumor activity (ORR: 20.0%, 95% confidence interval: 5.7% to 44.9%) in patients with “HER2-normal” breast cancer, defined as a HER2 fluorescence in situ hybridization ratio less than 2.0 and IHC ≤ 2+ [38].