The exploratory phase Ib/II PALOMA-1 trial and the confirmatory phase III PALOMA-2 trial demonstrated a significant difference in progression-free survival (PFS) in HR+/HER2– advanced breast cancer (ABC) patients receiving palbociclib plus letrozole versus letrozole alone, which resulted in accelerated approval of the combination therapy by the FDA [41,42,43,44]. Here, ERBB2 is linked to breast cancer.