CDK4 and breast cancer: Currently, four large international clinical trials (PALLAS (NCT02513394), MONARCHE (NCT03155997), NATALEE (NCT03701334), and ADAPTcycle (EudraCT 2018-003749-40)) are evaluating the combined treatment of a CDK4/6 inhibitor with endocrine therapy for the duration of 2–3 years in patients with intermediate to high-risk HR-positive/HER2-negative early breast cancers.