CDK4 and breast cancer: Most patients belonged to a high-ROR group at baseline (85% and 89%), and at surgery 46.9% (95% CI, 32.5–61.7) of patients in the ribociclib-plus-letrozole group and 46.1% (32.9–61.5) of patients in the chemotherapy group were low ROR; therefore, some patients with high-risk, early-stage ER+ breast cancer could achieve a molecular downstaging with CDK4/6 inhibitors and endocrine therapy.