An Open Label, Randomized, Multicenter Study Comparing the Efficacy and Safety of the Combination of Lasofoxifene and Abemaciclib to the Combination of Fulvestrant and Abemaciclib for the Treatment of Pre- and Postmenopausal Women and Men With Locally Advanced or Metastatic ER+/HER2- Breast Cancer With an ESR1 Mutation

This study is looking for a more effective way to treat breast cancer that has spread and has a specific genetic change called an ESR1 mutation. It compares two different drug combinations to see which one works better for patients who have already tried other common treatments.

This study is open to men and women whose breast cancer is ER+/HER2- and has grown after previous treatments like CDK inhibitors. You must have the ESR1 genetic mutation to be eligible for this specific trial.

Participants will be randomly assigned to one of two treatment groups, both of which involve taking a targeted pill called abemaciclib twice a day. Depending on your group, you will also take either the oral medication lasofoxifene or receive regular hormone-blocking injections of fulvestrant.

This study is currently recruiting volunteers at locations in Scottsdale and Tucson, Arizona, as well as Santa Rosa, California. It is a Phase 3 study, which means it is in the final stages of testing before a potential new treatment is approved.