Measuring them precisely is of utmost importance to clinical practice as these are presently the only validated breast cancer predictive biomarkers available, and they are routinely used to make decisions about patient treatment [6, 59].When comparing the expression levels of these three genes as defined by microarray and RNA-Seq, we found excellent Spearman correlation coefficients: 0.973 for ER [95% CI: 0.971-0.975]; 0.95 for PgR [95% CI: 0.947-0.954]; and 0.918 for HER2 [95% CI: 0.912-0.923] (Figure 2). This evidence concerns the gene ESR1 and breast cancer.