After trastuzumab monotherapy, there was a statistically significant upregulation of nuclear HER4 expression in the tumour biopsies collected at day 21 compared to the biopsies from the initial diagnosis (mean HER4 IRS at day 21=3.20, 95%CI = 1.84−4.56 vs. mean HER4 IRS at baseline=0.80, 95%CI=−0.56−2.16, p=0.025) (Figure 7D). This evidence concerns the gene ERBB4 and neoplasm.