GREB1 and metastatic neoplasm: To corroborate these observations we analyzed RNA-seq data in our cohort of longitudinal ER+ patient–matched primaries and metastatic tumors (bone and brain; n = 34), where we observe a decrease in ESR1 expression (P = 0.0371) and its target gene GREB1 (P = 0.0137) on metastasis, with no loss detected in AIB1 mRNA expression (P = 0.097) (Fig. S1D).