ERBB2 and breast cancer: In the MonarcHER phase II trial, patients with HR-positive, HER2-positive advanced breast cancer previously treated with at least two lines of anti-HER2 therapy were treated with a combination of abemaciclib with trastuzumab and fulvestrant, a selective estrogen receptor degrader (group A), abemaciclib and trastuzumab (group B), or the standard of care with trastuzumab and the physician’s choice of chemotherapy (group C).