This clinical trial is focused on studying the treatment of breast cancer, specifically in patients who have a type of breast cancer known as ER+/HER2-. This means the cancer cells have receptors for estrogen but not for a protein called HER2. The study is investigating a medication called elacestrant, which is being compared to standard endocrine therapy. Endocrine therapy is a treatment that blocks or lowers the amount of hormones in the body to slow down or stop the growth of cancer. The purpose of the study is to see if elacestrant can delay the spread of cancer to other parts of the body or prevent death in patients who have a relapse detected by a test called ctDNA, which looks for cancer DNA in the blood.

Participants in the study will be randomly assigned to receive either elacestrant or one of the standard endocrine therapies, which include medications like tamoxifen, anastrozole, exemestane, and letrozole. Some patients may also receive additional treatments such as leuprorelin, goserelin, or triptorelin, which are used to lower hormone levels in the body. The study will last for a period of up to 104 weeks, during which the effects of the treatments will be monitored. The study aims to determine which treatment is more effective in preventing the cancer from spreading or causing death.

Throughout the study, participants will have regular check-ups and tests to monitor their health and the progress of the treatment. These tests may include imaging scans like MRI or CT scans, which use magnetic fields or X-rays to create detailed pictures of the inside of the body. The study will also collect information on the safety of the treatments and how they affect the quality of life of the participants. The results of this study could help improve treatment options for patients with this type of breast cancer in the future.