Perlmutter Cancer Center

The purpose of this study is to evaluate whether SAR439859 (a novel hormonal treatment) is a better option compared to Letrozole (a standard hormonal treatment), when given in combination with Palbociclib (Ibrance®), in terms of efficacy and tolerance for treating your disease. SAR439859 is a potent, orally bioavailable, and selective estrogen receptor alpha (ERa) inhibitor that belongs to the selective estrogen receptor degrader (SERD) class of compounds. The study drug SAR439859 is investigational, which means that it has not been approved by the U.S Food and Drug Administration (FDA), the health authority that gives approval for new medicines to be prescribed in the United States, but the FDA has given its permission to test this agent in the current trial.