ERBB2 and breast cancer: In detail, for CDK4/6 inhibitors, The MonarchE trial [70], enrolling 5637 patients with ER+/HER2–negative early-stage BC at high risk of recurrence according to tumor size, grade, ki67 expression and N status showed that adjuvant Abemaciclib for 2 years plus ET vs. ET alone improved IDFS (invasive disease-free survival) (HR 0.75 95% CI 0.60–0.93 p = 0.01) and DRFS (disease recurrence-free survival) (HR 0.72 95% CI 0.56–0.92 p = 0.01).