ESR1 and invasive breast carcinoma: Using these markers, IHC analysis of 10,159 invasive breast cancers collected from 12 studies [8] showed that in addition to 77% of tumors classified as luminal based on ER and/or PR positivity, approximately 6% are non-luminal but overexpress HER2 protein or its amplified gene [9], and approximately 16% are basal-like or triple-negative (TN) because they lack ER, PR and HER2.