ESR1 and breast cancer: This observation was also confirmed by the analysis of the MSK breast cancer dataset (n = 438; age range, 23–92 years; median, 52 years) that we employed as an external additional control group (ER+ n = 395, 90.2%; PgR+ n = 342, 78.1%), as shown in Figure 2A. Furthermore, the prevalence of the HR+/HER2– phenotype was significantly lower in PrBC (p < 0.01), with EOBC showing an intermediate frequency compared to MSK in all subgroups of breast cancers (p < 0.01), as shown in Figure 2B and Supplementary Table S2.