Objective response during first-line treatment by investigator assessment by biomarker subgroups. The odds ratios and 95% CIs for objective response rates are shown by HER2 mRNA subgroup (that is, below the median versus equal to or greater than the median, and by quartile). HER2, human epidermal growth factor receptor 2; HT, trastuzumab plus docetaxel; max, maximum; min, minimum; T-DM1, trastuzumab emtansine. *Odds ratio is defined as complete or partial response determined on two consecutive tumor assessments at least 4 weeks apart based on the response evaluation criteria in solid tumors . Odds ratio relative to trastuzumab plus docetaxel was estimated by logistic regression. It was defined as the ratio of the odds of having a response in the T-DM1 arm and the odds in the trastuzumab plus docetaxel arm.