ESR1 and breast cancer: Several of the mRNA within the PAM50 profile are key markers for molecular BC diagnostics, for example, ESR1, PGR, ERBB2, MKI67, EGFR, KRT5, KRT14, and KRT17. In combination with other selected mRNA, the so‐called Parker algorithm may be used to separate BC into four molecular subtypes (luminal A, luminal B, HER2, and basal‐like) (Parker et al., 2009).