ESR1 and invasive ductal breast carcinoma: In order to determine the cell-of-origin phenotype of breast cancers, we examined the co-expression of the 14 lineage markers in nearly two thousand human breast invasive ductal carcinoma (IDC) samples and found that 95 % of invasive ductal carcinomas have a pure luminal phenotype including ER+, HER2+ and TNBCs [23, 33].