ESR1 and cancer: Although this receptor can bind estrogenic compounds, thereby exerting a modulatory role on the functions of the oncogenic ERα, the other estrogen receptor subtype active in cancer cells, by dimerizing with it and thereby modifying its activity on target genes [16, 23], in the absence of ligand it exhibits significant effects in BC cells [24], including, among others, miRNA-mediated post-transcriptional regulation of the BC cell proteome [25].