Evaluation of Lasofoxifene Combined With Abemaciclib in Advanced or Metastatic ER+/HER2- Breast Cancer With an ESR1 Mutation

This is an open-label, multicenter, single-arm safety study evaluating the safety and tolerability of the lasofoxifene and abemaciclib combination for the treatment of pre- and postmenopausal women with locally advanced or metastatic ER+/HER2- breast cancer who have disease progression on first and/or 2nd lines of hormonal treatment for metastatic disease and have an ESR1 mutation.