In addition, abemaciclib has been approved as monotherapy in patients with metastatic hormone receptor-positive HER2-negative breast cancer that has progressed through hormone therapy and chemotherapy based on the results of the Monarch 1 single-arm phase 2 trial, which demonstrated an objective response rate (ORR) of 19.7%, median PFS of 6 months, and median overall survival of 17.7 months [75]. This evidence concerns the gene ERBB2 and breast cancer.