RB1 and breast cancer: Their development has been focused on HR+ BC, where underlying genomic (e.g. CCND1 amplification, CDK4 amplification, CDKN2A loss, intact RB1) and transcriptomic (ER‐ or PI3K‐dependent CCND1 overexpression and activity) features render higher sensitivity to the inhibition of the cyclinD‐CDK4/6 pathway.7, 8, 9, 10, 11, 12