ShortStop-HER2: Shortened Duration of Adjuvant Therapy in Patients with Early-Stage HER2+ Breast Cancer Who Achieve pCR After Neoadjuvant Chemotherapy with HER2 Blockade

The purpose of this study is to compare the effectiveness of 6 months of HER2-targeted medications (trastuzumab with or without pertuzumab) versus 12 months of HER2-targeted medications at reducing the risk of breast cancer coming back or death in patients with early-stage HER2+ breast cancer who had a pCR after preoperative chemotherapy combined with trastuzumab. This study will help the study doctors find out if this different approach is better, the same, or worse than the usual approach. To decide if it is better, the study doctors will be looking to see if the study approach prevents your cancer from coming back compared to the usual approach. Post-surgery trastuzumab with or without pertuzumab is already approved by the FDA for use in early-stage HER2+ breast cancer. There will be about 1524 people taking part in this study.