monarcHER: A Phase 2, Randomized, Multicenter, 3-Arm, Open-Label Study to Compare the Efficacy of Abemaciclib Plus Trastuzumab With or Without Fulvestrant to Standard-of-Care Chemotherapy of Physician's Choice Plus Trastuzumab in Women With HR+, HER2+ Locally Advanced or Metastatic Breast Cancer

The purpose of this study is to evaluate the effectiveness of abemaciclib plus trastuzumab with or without fulvestrant versus trastuzumab plus physicians choice standard of care chemotherapy in women with hormone receptor positive (HR+), human epidermal growth factor receptor 2 positive (HER2+) locally advanced or metastatic breast cancer after prior exposure to at least two HER2-directed therapies for advanced disease. Overall survival data and the clinical study report (CSR) are not being shared due to immaturity of the data that mandates continued blinding of the trial.