ESR1 and breast cancer: We compared RS distribution and expression of single-gene/gene groups between a study group which consisted of estrogen receptor (ER) + HER2-negative BC patients with PVs in BRCA1/2 and the general 21-gene-tested BC patient population as reflected in a commercial use database (CDB) [16] and evaluated the associations between the RS result, single-gene/gene group expression, disease characteristics, and clinical outcomes in the study group.