To compare 2 types of standard care radiation treatment: photon and proton, to find out which type is best for treating non-metastatic breast cancer.
To demonstrate superiority of neoadjuvant T-DXd alone or in sequence with THP relative to ddAC-THP by assessment of pCR (ypT0/Tis ypN0) using central evaluation in participants with HER2-positive EBC
To compare the efficacy of abemaciclib in combination with fulvestrant to that of physician’s choice of chemotherapy in patients with HR+, HER2- metastatic breast cancer with at least 1 site of visceral metastases & at least 1 line of prior Endocrine Therapy.