ERBB4 and breast cancer: Patients in the validation set with high ERBB4-expressing breast cancer (cut-off value (log2 scale) = 1.3, the same as that used for the training set) had worse DRFS rates than those with low expression (5Y DRFS, low vs. high: 69.4 % vs. 44.7 %, p = 0.053) (Fig. 4b).