Esr1 Gene Mutation

The goal of this research study is to compare a combination of two drugs, capecitabine and elacestrant to capecitabine alone as a treatment for advanced estrogen receptor-positive (ER+) 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. The names of the study drugs involved in this study are: * Elacestrant (a type of selective estrogen receptor degrader) * Capecitabine (a type of fluoropyrimidine antimetabolite)

This trial will study a type of advanced breast cancer (ABC) defined as endocrine receptor (ER)-positive/human epidermal growth factor receptor 2(HER2)-negative and estrogen receptor 1 (ESR1)-mutated. Patients will be treated with elacestrant, a compound that acts as a selective estrogen receptor degrader, and everolimus (or placebo), a kinase inhibitor indicated for the treatment of postmenopausal women with advanced hormone receptor-positive, HER2-negative breast cancer. The main purpose of the study is to analyze the efficacy (to find out how effective a treatment is) of elacestrant plus everolimus therapy in patients who have ER-positive/HER2-negative, ESR1-mutated, ABC progressing to endocrine therapy and cyclin-dependent kinase 4/6 (CDK4/6) inhibitor. The efficacy of elacestrant plus everolimus combination will be determined by assessing the period from elacestrant plus everolimus (or placebo) treatment initiation until to the first occurrence of disease progression, unacceptable toxicity, death, or discontinuation from the study treatment for any other reason, whichever occurs first, defined as progression free survival. Rigorous eligibility criteria based on specific co-morbidities and clinicopathologic features of their disease have been designed to minimize the risk of patients participating in this study. The anticipated favorable clinical benefits of elacestrant combined with everolimus are projected to outweigh the risks of this treatment. This study will be performed in full compliance with International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) and all applicable local Good Clinical Practice (GCP) and regulations.

Despite broad advancements in endocrine therapy for ERα+ breast cancer, resistance ultimately develops. A common driver of resistance are known ESR1 mutations that lead to constitutively active receptor signaling and transcriptional regulation that is always "turned on" despite the absence of estrogen. Patients with ESR1 mutations are expected to have decreased binding affinity for tamoxifen and thus may be underdosed on standard therapy. \[18F\]-fluoroestradiol Positron Emission Tomography/Computed tomography (FES-PET/CT) imaging is a novel functional imaging technique that can non-invasively measure ERα expression and inhibition in metastatic ERα+ breast cancer. The proposed a pilot study uses FES-PET/CT imaging to measure ERα blockade to determine the optimal dose of tamoxifen in patients with ESR1 mutations.

This is a prospective, non-interventional real-world study to observe the efficacy and safety of different treatment regimens in patients with ESR1-mutated HR+/HER2-advanced breast cancer after failure of endocrine therapy. Epidemiological data, efficacy and safety measures will be collected for each subject. Data on efficacy and safety assessment indicators will be collected every 2-3 months until disease progression, receipt of a new anti-tumour treatment modality, death, loss to follow-up, and arrival at the data collection cut-off date. The cut-off date for data collection is defined as 8 weeks after completion of 6 visits for each subject, or 4 weeks after treatment discontinuation and subject discontinuation/withdrawal. Subjects receiving a different treatment regimen remained subject to assessment of safety indicators 4 weeks after discontinuation of the original treatment regimen.

This study is a prospective non-interventional real-world study enrolling patients with advanced breast cancer who are ER+/HER2- and have ESR1- gene mutations, collecting information on patients' complaints, physical examination, laboratory tests, imaging tests and adverse events to observe the safety of elacestrant treatment.