About the Study Therapies

What are the study therapies?

You may receive 1 of 2 therapy combination options. Half of the study participants receive a combination of the investigational therapy lasofoxifene and abemaciblib. The other half of study participants receive a combination of fulvestrant and abemaciclib. Learn more about each therapy below:

The investigational therapy: lasofoxifene

  • The investigational therapy is called lasofoxifene. Investigational means lasofoxifene is not yet approved by any health or regulatory agency for treating ER-positive/HER2-negative metastatic breast cancer with an ESR1 mutation. It is being studied in the ELAINE-3 study.
  • Lasofoxifene is an investigational oral medication that demonstrates tissue selective activity. In breast cancer cells bearing an estrogen receptor mutation (ESR1 mutation), lasofoxifene turns off these receptors while turning on estrogen receptors in other tissues such as bone and vaginal tissue.
  • Lasofoxifene is a tablet taken once a day with or without food.
  • Lasofoxifene has been investigated in metastatic breast cancer in two previous studies: ELAINE-1 and ELAINE-2. Learn more about these studies and the results here.


  • Participants in the study who are not assigned to receive lasofoxifene receive fulvestrant, an approved cancer therapy. Fulvestrant is another type of hormone therapy that blocks the effects of estrogen in the body. Limiting the amount of estrogen in the body can slow cancer growth.
  • Fulvestrant is 2 injections (shots) given into the muscle of the buttocks on Days 1, 15 and 29 and then once monthly thereafter.


  • All participants in the study receive abemaciclib, an approved cancer therapy often given in combination with fulvestrant. Abemaciclib is known as a kinase inhibitor. It works by blocking a protein that signals for cancer cells to multiply. Without this signal, cancer cells do not grow as fast.
  • Abemaciclib is a tablet taken twice a day with or without food.