This study is for people with a type of breast cancer called ER+/HER2- metastatic breast cancer. Metastatic means the cancer has spread to other parts of the body. The study has two phases. Phase 1b finds a safe dose of a new drug called elacestrant when taken with other cancer drugs like alpelisib, everolimus, and ribociclib. Phase 2 checks how well these combinations work and how safe they are. The study will have 400 participants across different treatment groups. Each group gets a different combination of drugs, and the study tracks their effects.

• The study might need you to take medication combinations and visit the hospital regularly.
• There are strict eligibility criteria, including no previous use of elacestrant.
• Participants might help find better treatments for advanced breast cancer.