Tailoring NEOadjuvant Therapy in Hormone Receptor Positive, HER2 Negative, Luminal Breast Cancer.

Based on Ki67 levels after two weeks of initial letrozole treatment in postmenopausal patients with hormone receptor positive, HER2 negative, stage II/III breast cancer, patients are either advised to continue letrozole treatment (if Ki67 \<1%) or will be randomized between standard chemotherapy (AC-T) or ribociclib in combination with letrozole (if Ki67 ≥1%).