The monarchE trial [26,87] randomly assigned 5637 high risk patients—defined as patients with four or more positive nodes, or one to three nodes and either tumor size ≥5 cm, histologic grade 3, or central Ki-67 ≥20%—to either standard-of-care adjuvant endocrine therapy alone (n = 2829), or standard-of-care adjuvant endocrine therapy plus the CDK 4/6 inhibitor abemaciclib (n = 2808). This evidence concerns the gene MKI67 and neoplasm.