Phase 2 Study of Amcenestrant (SAR439859) Versus Physician's Choice in Locally Advanced or Metastatic ER-positive Breast Cancer

Inclusion criteria : * 18 years or older. * Histological or cytological diagnosis of adenocarcinoma of the breast. * Locally advanced not amenable to radiation therapy or surgery in a curative intent, and/or metastatic disease. * Estrogen receptor(ER) positive status. * Human epidermal growth factor receptor 2 negative status. * Participants must have received no more than 1 prior chemotherapeutic or 1 targeted therapy regimen for advanced/metastatic disease. * In the main study, a prior treatment with a Cyclin-dependent kinase 4 and 6(CDK 4/6) inhibitor is mandatory if this treatment is approved and can be reimbursed for this participant. The percentage of participants without previous CDK 4/6 inhibitor will be capped to 20%. In the Chinese extension cohort, previous treatment with a CDK 4/6 inhibitor will not be mandatory, and there will be no limitation to the number of participants naïve to CDK4/6 inhibitor. * Participants must present a secondary endocrine resistance to endocrine therapy defined as: progression while on endocrine therapy after at least 6 months of treatment for advanced breast cancer, or relapse while on adjuvant endocrine therapy but after the first 2 years, or with a relapse within 12 months after completing adjuvant endocrine therapy. * Male or Female. Exclusion criteria: * Eastern Cooperative Oncology Group performance status =\>2. * Medical history or ongoing gastrointestinal disorders potentially affecting the absorption of amcenestrant. Partici…