ERBB2 and breast cancer: Importantly, when variables correlating with univariate survival at p < 0.20 were later included in multivariate Cox regression analysis (Table 4), the presence of the basal 2-HER2+ phenotype (i.e., a positive CK5/6 staining in more than 10% of the HER2+ breast cancer tissue sections) retained its independent value for predicting a worse outcome in terms of DFS (hazard ratio 2.44, 95% confidence interval 1.05–5.67; P = 0.037).