ESR1 and cancer: This study, which compared RS results, single-gene expression of the 16 cancer genes within the 21-gene assay, and gene group scores between a cohort of ER + BC patients with PVs in BRCA1/2 (N = 81) and all 21-gene-tested BC patients (N = 799,986) demonstrated that those with PVs in BRCA1/2 had higher RS results that could not be attributed to menopausal status or age at diagnosis and stemmed from a distinct gene expression profile of the majority of these 16 cancer genes.