ESR1 and breast cancer: In the NeoPalAna trial, patients with stage II/III ER+/HER2neg primary BC received neoadjuvant palbociclib and anastrozole.23 Serial biopsies performed at baseline (C0D1), before starting palbociclib (C1D1) and after 2 weeks of palbociclib (C1D15), and surgical samples were analyzed for Ki67, GE, and mutation profiles.23 We found that CCNE1/RB1 was significantly higher in patients resistant to palbociclib at C0D1, C1D1, C1D15 (p(WMW) = 0.0048; p = 0.013; p = 0.032, respectively, Fig. 6d).