NEOadjuvant Abemaciclib and GIredestrant TriaL in Patients with ER-positive, HER2-negative Early Breast Cancer

The objective of the study is to evaluate the efficacy and the safety of abemaciclib and giredestrant before surgery in participants with early stage, oestrogen receptor-positive (ER+), human epidermal receptor 2 negative (HER2-) breast cancer (BC). Primary objective: ● To evaluate the efficacy of abemaciclib and giredestrant in complete cell cycle arrest (CCCA) rate at Week 2. Secondary objectives: * To evaluate the efficacy of abemaciclib and giredestrant in reducing the relative Ki67 expression from baseline to Week 2 * To evaluate the efficacy of abemaciclib and giredestrant in risk of recurrence (ROR) score reduction, clinical and radiological tumor response; * To evaluate the safety of abemaciclib and giredestrant. Exploratory objectives: * To evaluate the mechanisms of response and resistance to therapy; * To evaluate the correlation between Ki-67% reduction and 18- Fluorothymidine (FLT) uptake reduction; * To evaluate the pathological complete response (pCR) rate (ypT0/is, ypN0) of giredestrant plus abemaciclib