ERBB2 and breast cancer: Initially, the PALOMA-1/TRIO-18 trial demonstrated a PFS prolongation of ten months (20.2 months vs. 10.2 months, HR 0.49, p = 0.0004) by adding palbociclib to letrozole compared to a letrozole monotherapy in patients with advanced ER-positive and HER2-negative BC [19].