ESR1 and breast cancer: Luo et al.23 reported that 28% of 137 primary TNBC were AR+ (≥1% cells staining) and Collins et al. 24 reported 31% AR positivity (>10% cells staining) in 216 primary basal breast cancers, defined as ER, PR and HER2-negative with either CK5/6 or EGFR expression by IHC staining.