ESR1 and breast cancer: Although HER2 and uPAR were described as independent tumor-specific protein predictors of BC progression for decades, correlative expression of HER2 and uPAR was first reported by Pierga et al., [32] who found a high level of correlation between HER2 and uPAR mRNA in disseminated tumor cells (DTC) in 8 out of 16 patients (50%) and was associated with a more aggressive primary tumor phenotype (estrogen receptor (ER)-negative, progesterone receptor (PR)-negative or HER2-positive).