This is a prospective, single-arm, phase II study of 32 evaluable patients treated with NEOADjuvant Aromatase inhibitor and Pertuzumab/Trastuzumab (NEOADAPT) without chemotherapy for hormone receptor positive (HR+), [i.e. Estrogen Receptor positive (ER+) and/or Progesterone Receptor positive (PR+)] HER2+ localized, non-metastatic stage I - IIb breast cancer.

Inclusion Criteria:

• Ability to provide signed, written informed consent
• Histologically or cytologically confirmed non-metastatic adenocarcinoma of the breast (stage I-II)
• Candidate for curative-intent treatment
• ER+ and/or PR+ and HER2-positive (Fluorescence In Situ Hybridization-positive or 3+ by Immunohistochemistry staining)
• Life expectancy greater than 5 years
• Left Ventricular Ejection Fraction > 50% at baseline (within 30 days of day 0)
• Eastern Cooperative Oncology Group performance status ≤2
• Absolute Neutrophil Count >1000/µL
• Platelets ≥50,000/µL
• Hemoglobin >8.0 g/dL,
• Creatinine ≤3.0 x upper limit of normal (ULN)
• Bilirubin ≤3.0 x ULN
• Aspartate aminotransferase or Alanine aminotransferase <5.0 x ULN
• Negative serum pregnancy test for women <12 months after the onset of menopause unless surgically sterilized
• Agreement by women of childbearing potential and male participants with partners of childbearing potential to use a "highly effective", non-hormonal form of contraception or two "effective" forms of non-hormonal contraception by the patient and/or partner.

Exclusion Criteria:

• Active infection
• Presence of known metastases (stage IV disease)
• Pregnant or lactating women
• Prior chemotherapy or radiation therapy for the primary breast cancer
• Concomitant malignancies or previous malignancies within the last 5 years except adequately treated basal or squamous cell carcinoma of the skin or carcinoma in situ of the cervix.
• History of significant cardiac disease, cardiac risk factors or uncontrolled arrhythmias
• Current severe, uncontrolled systemic disease (e.g., clinically significant cardiovascular, pulmonary or metabolic disease including diabetes, wound healing disorders, ulcers or bone fractures)
• Major surgical procedure or significant traumatic injury within 28 days prior to study treatment start or anticipated need for major surgery during the course of study treatment
• Current known infection with Human Immunodeficiency Virus (HIV), Hepatitis B virus (HBV) or Hepatitis C Virus (HCV)
• Receipt of intravenous antibiotics for infection within 14 days prior to receiving study treatment
• Current chronic daily treatment with corticosteroids (dose >10 mg/day methylprednisolone equivalent) except inhaled steroids
• Known hypersensitivity to any of the study drugs
• Assessment by the investigator to be unable or unwilling to comply with the requirements of the protocol