IGF-1 levels decreased by 41% with ADT+E4 versus an increase of 10% with ADT+placebo (p < 0.0001). The almost complete suppression of the tumor stimulator FSH using ADT plus E4 observed in all individual patients in this study, along with the augmented suppression of IGF-1 versus an increase by ADT only, may be clinically relevant and suggest the enhanced anti-cancer treatment efficacy of E4 in addition to the previously reported additional suppression of total and free T and PSA.
This review summarizes the characterization of the pharmacological properties of E4 as well as recent advances made in the understanding of the molecular mechanisms of action driving its activity. How the unique mode of action and the different metabolism of E4 might support its favorable benefit-risk ratio is also discussed.
E4 has a small effect on normal breast tissue proliferation and minimally affects hepatic parameters. This distinct profile of ERα activation, uncoupling nuclear and membrane activation, is unique.