ERBB2 and breast carcinoma: In our analyses of BrM, AR is most frequently expressed in HER2+ BrM (previously reported to be expressed in 76–87% of primary HER2+ breast cancers [3,19,20]), and AR is least frequently expressed in TNBC BrM (previously reported to be expressed in 27–35% of primary TNBC) [3,5,7].