ESR1 and breast cancer: The second study end point was to compare the quantitative Xpert® Breast Cancer STRAT4 dCt results for each marker with the percentage staining results by IHC for ER, PgR and Ki-67 as well as HER2 categorical results (negative = IHC 0, 1+, 2+/ISH non-amplified versus positive = IHC 3+ or IHC 2+/CISH amplified).