The purpose of this study is to learn more about an experimental drug called Imlunestrant, which may be helpful in treating early breast cancer. Researchers are hoping to find out how Imlunestrant compares to standard of care endocrine therapies. Therefore, there are two study groups: one group will receive Imlunestrant, and the other group will receive one of the following FDA approved endocrine therapies: Anastozole, Tamoxifen, Letrozole, or Exemestane. If you agree and are eligible to partipate in the study, you will be randomly assigned to one of the two groups, like flipping a coin. You and your medical provider cannot choose which group you are assigned to. You will know what drug you have been selected to recieve.