Endocrine Therapy Response and 21-Gene Expression Assay for Therapy Guidance in HR+/HER2- Early Breast Cancer.

To our knowledge, WSG-ADAPT-HR+/HER2- (ClinicalTrials.gov identifier: NCT01779206; n = 5,625 registered) is the first trial combining the 21-gene expression assay (recurrence score [RS]) and response to 3-week preoperative endocrine therapy (ET) to guide systemic therapy in early breast cancer. Baseline and postendocrine Ki67 (Ki67 Intention-to-treat population comprised 2,290 patients (n = 1,422 experimental WSG-ADAPT-HR+/HER2- demonstrates that guiding systemic treatment by both RS and ET response is feasible in clinical routine and spares CT in pre- and postmenopausal patients with ≤ 3 involved lymph nodes.