Barcelona researchers at the Hospital Clínic-IDIBAPS Research Institute, the University of Barcelona and the SOLTI academic cancer research group have shown that the molecular classification of breast cancer, which divides it into four subtypes (Luminal A, Luminal B, HER2-enriched and Basal-like) is useful for predicting the benefits of treatment in patients with advanced hormone-sensitive breast cancer. This is the largest study to have shown the value of the biomarker, and the first to do so in the context of a CDK4/6 inhibitor like ribociclib.