ERBB2 and breast cancer: In the MONARCH 2 trial, abemaciclib plus fulvestrant significantly improved the PFS (median 16.4 vs. 9.3 months) and ORR (48.1% vs. 21.3%) compared with placebo plus fulvestrant and exhibited a good safety profile in patients with HR+, HER2– advanced breast cancer who had progressed while receiving ET (8).