Abemaciclib plus trastuzumab with or without fulvestrant versus trastuzumab plus standard of-care chemotherapy in women with HR+, HER2+ advanced breast cancer: plain language summary of the monarcHER trial

What is this summary about? This article summarizes the results of a study called monarcHER. The study included participants with a certain type of aggressive breast cancer called HR+, HER2+ advanced breast cancer (ABC) that had their disease worsen or return after multiple previous therapies. This summary intends to help you understand the impact of a non-chemotherapy treatment called abemaciclib in people with HR+, HER2+ ABC. When the study was planned, HER2-targeted therapy (i.e., trastuzumab) was standard treatment and was typically combined with chemotherapy and endocrine therapy (i.e., fulvestrant). However drug resistance can develop when HER2+ targeted therapy is used for a long time, making it less effective and allowing cancer to grow or spread to other parts of the body. When this happens, few chemotherapy-free options are available. Because of the chemotherapy side effects, this is not desirable. There is an urgent need to develop new, effective, safe and tolerable treatment options for patients with HR+, HER2+ ABC. The monarcHER study compared the effects of abemaciclib plus trastuzumab with or without fulvestrant to the standard of care treatment.