Oestrogen is synthesised, catalysed by aromatase, and subsequently binds to the estrogen receptor (ER) alpha/beta subunits which dynamically interact with the estrogen responsive elements (ERE) in the promoter region of miR-191 [39], increasing expression and driving proliferation, migration and chemoresistance in several cancer types [54, 66–68]. The gene discussed is CYP19A1; the disease is cancer.