This is a multicenter, Phase 1b/2 trial in participants with estrogen receptor positive/human epidermal growth factor receptor 2 negative (ER+/HER2-) advanced/metastatic breast cancer. The phase 1b part of the trial will determine the recommended Phase 2 dose (RP2D) of elacestrant when administered in combination with alpelisib, everolimus, palbociclib, capivasertib, and ribociclib. The Phase 2 part of the trial will evaluate the efficacy and safety of the various combinations.