PhII Randomized CAPecitabine + ELAcestrant vs. Capecitabine Alone in ER+ Breast Cancer (CAPELA)

This is a Phase II, multi-center, open-label, randomized study comparing a combination of two drugs, capecitabine and elacestrant, to capecitabine alone as a treatment for advanced estrogen receptor-positive (ER+) Human Epidermal Growth Factor Receptor 2 negative (HER2-) breast cancer. This study is designed for participants with cancer that has previously stopped responding to medication in the class of therapy called CDK 4/6 inhibitors, including palbociclib, ribociclib, or abemaciclb. Participants will be randomized into one of two study groups: Arm A Capecitabine and Elacestrant versus Arm B Capecitabine alone. Randomization means a participants is placed into a study group by chance. The U.S. Food and Drug Administration (FDA) has approved capecitabine as a treatment option for advanced estrogen receptor-positive (ER+) Human Epidermal Growth Factor Receptor 2 negative (HER2-) breast cancer. The FDA has approved elacestrant for metastatic breast cancer with an ESR1 mutation. Elacestrant is not FDA approved for participants whose cancer does not have ESR1 mutation and it is possible elacestrant may not be as effective or effective at all in participants whose tumors do not have an ESR1 mutation. The FDA has not approved Elacestrant and Capecitabine to be given together. The research study procedures include screening for eligibility, in-clinic visits, questionnaires, blood tests, urine tests, Computerized Tomography (CT) scans, Magnetic Resonance Imaging (MRI) scans, and electrocardiograms (ECGs). It is expected that about 297 people will take part in this research study. Stemline, a Menarini Group Company, is supporting this research study by providing the study drugs, elacestrant, and funding. This study is also being supported by Johns Hopkins University on behalf of the Translational Breast Cancer Research Consortium (TBCRC).