A Single Arm Phase II Study of ADjuvant Endocrine Therapy, Pertuzumab, and Trastuzumab for Patients With Anatomic Stage I Hormone Receptor-positive, HER2-positive Breast Cancer

The research study procedures include screening for eligibility and study treatment including laboratory evaluations, physical exams, questionnaires, and follow up visits. * Participants will receive HER2-directed treatment for 1 year and hormonal therapy for approximately 5 years. * It is expected that about 375 people will take part in this research study. This research study is a Phase II clinical trial. Phase II clinical trials test the safety and effectiveness of an investigational drug combination to learn whether the drug works in treating a specific disease. "Investigational" means that the drug combination is being studied. The drugs trastuzumab and pertuzumab are both monoclonal antibodies, which are disease-fighting proteins made by cloned immune cells. The U.S. Food and Drug Administration (FDA) has approved trastuzumab, pertuzumab, and trastuzumab + pertuzumab subcutaneous fixed dose combination (PHESGO) as treatment for HER2 positive breast cancer. The FDA has also approved hormonal therapies as treatment for hormone receptor positive breast cancer. .