ESR1 and breast cancer: Moreover, evaluating miR-205 expression in a panel of cell lines belonging to the highly aggressive triple-negative [estrogen receptor (ER), progesterone receptor (PR) and Her2/neu] breast cancer subtype, which still lacks an effective targeted therapy and is characterized by an extremely undifferentiated mesenchymal phenotype, the authors demonstrated that this miRNA is critically downregulated compared with a normal cell line.