Prat A, Saura C, Pascual T, et al. - Researchers conducted this open-label, multicentre, randomised, phase 2 trial to assess the biological and clinical activity of neoadjuvant ribociclib plus letrozole in the luminal B subtype of early stage breast cancer. This trial was completed across 21 hospitals in Spain. Study participants included postmenopausal women (≥ 18 years) with stage I–IIIA hormone receptor-positive, Eastern Cooperative Oncology Group Performance Status 0–1, HER2-negative breast cancer and luminal B by PAM50 with histologically confirmed, operable primary tumour size of at least 2 cm in diameter as measured by MRI. Participants in the study were randomly assigned (1:1) using a web-based system and permuted blocks of 25 to receive either six 28-days cycles of ribociclib (oral 600 mg once daily for 3 weeks on, 1 week off) plus daily letrozole (oral 2·5 mg/day) or four cycles of doxorubicin (intravenous 60 mg/m²) and cyclophosphamide (intravenous 600 mg/m²) every 21 days followed by weekly paclitaxel (intravenous 80 mg/m²) for 12 weeks. One hundred six patients were enlisted between July 27, 2017, to December 7, 2018. Findings suggested that with CDK4/6 inhibitor and endocrine therapy, some individuals with high-risk, early-stage, hormone receptor-positive, HER2-negative breast cancer could achieve molecular downstaging of their disease. Neutropenia, febrile neutropenia and elevated alanine aminotransferase concentrations were the most common grade 3–4 adverse events. There were no deaths found during the study.