Patients with breast cancer, who have completed first line therapy (e.g., radiotherapy, chemotherapy, surgery), and who have to be identified with having a high risk of recurrence of cancer, will be eligible for the study. This patient group is currently offered a standard of care chemotherapy plus endocrine therapy (ET). The study investigates whether the patient group with high-risk early breast cancer benefits from treatment with the medication abemaciclib in combination with ET compared to ET alone.

The WSG ADAPT trial program is one of the first new generation trials addressing the issue of individualization of (neo)-adjuvant decision-making in early breast cancer (EBC) in a subtype-specific manner. The first WSG ADAPT umbrella trial (NCT01779206) aimed to establish early predictive molecular surrogate markers for response after a short 3-week induction treatment. The goals of the WSG ADAPT trial program - early response assessment and subtype-specific therapy tailoring to those patients who are most likely to benefit - have contributed to the positive national and international feedback regarding the ADAPT-concept as a whole. The aim of this ADAPTlate phase-III-trial is to gain further knowledge of the group of patients at intermediate to high risk for disease recurrence, who have completed definite locoregional therapy (with or without neoadjuvant or adjuvant chemotherapy). With ADAPTlate it is planned to investigate if the intermediate to high-risk patient group identified during the screening phase derives additional benefit from treatment with abemaciclib in combination with ET compared to ET alone.