Summary
The goal of this clinical trial is to assess the efficacy, safety and tolerability of the
combination of lasofoxifene and abemaciclib compared to fulvestrant and abemaciclib for
the treatment of pre- and postmenopausal women and men who have previously received
ribociclib or palbociclib-based treatment and have locally advanced or metastatic
estrogen receptor positive (ER+)/human epidermal growth factor 2 negative (HER2-) breast
cancer with an estrogen receptor 1 (ESR1) mutation.
The main question the study aims to answer is:
• To compare the efficacy of the combination of lasofoxifene and abemaciclib with that of
fulvestrant and abemaciclib Participants will receive either receive 5 mg/d of oral
lasofoxifene plus oral abemaciclib 150 mg twice a day or the combination of fulvestrant
500 mg intramuscular (IM) on Days 1, 15, and 29 and then once monthly thereafter plus
oral abemaciclib 150 mg twice a day.