In breast cancer, miRNAs regulate genes involved in apoptosis, cell-signaling pathways (e.g., TGFβ [220], epithelial-to-mesenchymal transformation (EMT) [221], metastasis [222], the expression of ERα [117] and other nuclear receptors (NRs) [50]), regulation of the tumor microenvironment, and stemness, which includes transfer or exosomal miRNAs to adjacent normal fibroblasts forming cancer-associated fibroblasts (CAFs) (reviewed in [223]). Here, ESR1 is linked to breast cancer.