Phase 2 Window Study of SAR439859 (Amcenestrant) Versus Letrozole in Post-menopausal Patients With ER+, HER2- Pre-operative Post-menopausal Primary Breast Cancer

Primary Objective: To determine whether amcenestrant given at 2 different doses improved the antiproliferative activity when compared to letrozole. Secondary Objectives: * To assess the proportion of participants with a relative decrease from Baseline in percentage of positive tumor cells tested by immunohistochemistry greater than or equal to (\>=) 50 percent (%) (Ki67 \>=50%) in the three treatment arms. * To assess estrogen receptor (ER) degradation in biopsies in participants in the three treatment arms. * To assess safety in the three treatment arms.