HER2 staining heterogeneity was significantly higher for discordant cases compared to concordant cases based on pathologist defined tumour cell percentages (concordant cases: median = 0.42, N = 59; discordant cases: median = 0.69, N = 12; W = 186, p = 0.01, Wilcoxon rank sum test; Fig. 6a) and based on tumour cell percentages defined by automated image analysis (concordant cases: median = 0.71, N = 59; discordant cases: median = 1.04, N = 12; W = 162, p = 0.003, Wilcoxon rank sum test; Fig. 6b). Here, ERBB2 is linked to neoplasm.