To address this issue, several ongoing studies are randomizing patients to either endocrine therapy alone or in combination with CDK4/6 inhibitor treatment, based on postoperative ctDNA, disseminated breast cancer cells of bone marrow, or changes in Ki-67 during induction therapy (NCT03285412, NCT04567420, NCT04985266, NCT04841148). Here, MKI67 is linked to breast cancer.