Primary Objectives
To evaluate the progression free survival (PFS) 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.
Secondary Objectives
To evaluate the antitumor response of each drug regimen as characterized by:
• Objective response rate (ORR)
• Overall survival (OS)
• Clinical benefit rate (CBR)
• Duration of response (DoR) in subjects with an objective response
• Time to response (TTR) in subjects with an objective response
In addition, to determine the following for the study population:
• Time to cytotoxic chemotherapy
• Quality of life (QoL) using Functional Assessment of Cancer Therapy-Breast Cancer-Endocrine Subscale (FACT B-ES)
• Safety