FGFR4 and breast cancer: Yet, our analyses highlight three important aspects of FGFR4 in breast cancer, i) that heterogeneity in expression within HER2E tumors exists (e.g., Fig. 3I), ii) that heterogeneity in expression exists between PAM50 subtypes, with, e.g., high FGFR4 expressing tumors also in the PAM50 LumA and LumB subtypes (Fig. 3I), and iii) that the gene does not appear driven by copy number alterations or somatic alterations as underlined by the total absence of called FGFR4 amplifications or pathogenic somatic mutations in our WGS-analyzed ERpHER2n HER2E tumors.