In contrast, much higher numbers of breast tumor specimens have been analyzed in studies using multigene assays, such as the 70-gene assay (Mammaprint) (n = 6600) [159], the 21-gene assay (OncotypeDX) (n = 10,273) [160], the 50-gene assay (PAM50) (n = 2558) [161], and the 12-gene assay (Endopredict) (n = 2185) [162], and these genomic assays are used in everyday practice to guide clinical decision-making on whether or not to administer chemotherapy in early luminal A and B (estrogen-receptor-positive) breast cancer. This evidence concerns the gene ESR1 and breast neoplasm.