ESR1 and breast cancer: The same results were replicated in two independent validation datasets, the publicly available gene expression dataset “METABRIC”28 of fresh-frozen breast tissues and our targeted RNA-seq dataset “TARGETSEQ” of breast cancer FFPE tissues, in proliferation-high and ER-negative (Fig. 2c,e) or ER-positive groups (Fig. 2d,f), and proliferation-low groups (Supplementary Figure 3C, D and E).