To address the unmet need, we conducted a prospective phase II clinical trial (LEADER) which investigated the use of ribociclib in two different dosing schedules (600 mg vs 400 mg) and time of initiation (early, prior ET < 2 years vs delayed, prior ET ≥ 2 years) initiation with standard adjuvant ET for patients with HR+/HER2– early-stage breast cancer. Here, ERBB2 is linked to breast cancer.