Real-World Evidence of Ribociclib Plus Aromatase Inhibitors as First-Line Treatment in Advanced Breast Cancer: The BrasiLEEira Study.

Purpose: Cyclin inhibitors plus endocrine therapy represent the reference standard for hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) locally advanced or metastatic breast cancer (ABC). Efficacy results on hard end points such as overall survival come from well-designed randomized clinical trials (RCTs). However, a limitation of RCTs is the low external results validity, and their extrapolation to a broader population may not be appropriate.