ERBB2 and cancer: The marker discovery results (Figure 4a,b) clearly show the gene expression of the canonical markers of cancer epithelial cells for the HR-positive and HER2-positive subtypes, i.e., ESR1 [31], AGR2 [32] and AGR3 [33] in the HR-positive subgroup and ERBB2 [34] in the HER2-positive subgroup, indicating that the analysis is appropriate in this context.