Safety of Elacestrant in ER+/HER2- and ESR1 Mutations MBC

This study is testing a drug called elacestrant — a pill-form hormone therapy — for women with advanced or metastatic breast cancer that is estrogen receptor-positive (ER+), HER2-negative, and has a specific ESR1 gene mutation, which often develops after standard hormone treatments stop working. **You may be eligible if...** - You are a woman aged 18 or older with ER+/HER2- breast cancer that has spread locally or to distant sites - Your tumor has tested positive for an ESR1 mutation - Your cancer has progressed on at least one prior hormone therapy - You are postmenopausal or on ovarian suppression therapy **You may NOT be eligible if...** - Your tumor is HER2-positive or estrogen receptor-negative - You have not had prior endocrine (hormone) therapy - You have active or uncontrolled serious medical conditions Talk to your doctor to see if this trial is right for you.