Patient description: The patient is a 42 year-old postmenopausal woman who had a screening sonogram which revealed an abnormality in the right breast. She had no palpable masses on breast exam. Core biopsy was done and revealed a 1.8 cm infiltrating ductal breast carcinoma in the left upper outer quadrant. Lumpectomy was done and the surgical margins were clear. The tumor was HER2-positive and ER/PR negative. Axillary sampling revealed 1 positive lymph node out of 12 sampled. CXR was unremarkable. She is using “well women” multivitamins daily and no other medication. She smokes frequently and consumes alcohol occasionally. She is in a relation with only one partner and has a history of 3 pregnancies and live births. She breastfed all three children.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  HER2-positive Breast Cancer Invasive Carcinoma of the Breast Breast Cancer Node Negative Breast Cancer Micrometastasis Breast Cancer Hormone Receptor Positive Breast Cancer HER2-positive T1 histologically confirmed invasive carcinoma of the breast. Patients must have node-negative (N0) or micrometastases (N1mi) breast cancer according to the AJCC 8th edition anatomic staging table If the patient has had a negative sentinel node biopsy, then no further axillary dissection is required, and the patient is determined to be node-negative. Axillary nodes with single cells or tumor clusters ≤ 0.2 mm by either H&E or immunohistochemistry (IHC) will be considered node-negative Any axillary lymph node with tumor clusters between 0.02 and 0.2cm is considered a micrometastasis. Patients with a micrometastasis are eligible. An axillary dissection is not required to be performed in patients with a micrometastasis found by sentinel node evaluation. In cases where the specific pathologic size of lymph node involvement is subject to interpretation, the overall principal investigator will make the final determination as to eligibility. The investigator must document approval in the patient medical record Patients who have an area of T1aN0, ER+ (defined as ≥ 10%), HER2-negative cancer in either breast, in addition to their primary HER2 positive tumor, are eligible For unifocal disease, all invasive disease must have been tested for ER and PR (for multifocal disease, see below). Either ER or PR must be positive, defined as ER ≥10% or PR ≥10%. ER and PR-assays should be performed by immunohistochemical methods according to the local institution standard protocol HER2-positive by ASCO CAP 2018 guidelines, confirmed by central testing. See Appendix I for ASCO CAP 2018 HER2 testing guidelines NOTE: DCIS components will not be counted in the determination of HER2 status NOTE: HER-2 status must be confirmed to be positive by central review prior to patient starting protocol therapy. Patients previously having had HER2 testing by NeoGenomics do not need to undergo retesting for central confirmation of HER2 status. A pathology report documenting testing by NeoGenomics should be provided at time of patient registration Bilateral breast cancers that individually meet are allowed  Neoadjuvant or adjuvant chemotherapy for this breast cancer prior to enrollment is prohibited Any of the following due to teratogenic potential of the study drugs Pregnant women Nursing women Women of childbearing potential who are unwilling to employ adequate contraception (condoms, diaphragms, IUDS, surgical sterilization, abstinence, etc). Hormonal birth control methods are not permitted Men who are unwilling to employ adequate contraception (condoms, surgical sterilization, abstinence, etc) Participants who are receiving any other investigational agents for treatment of breast cancer, unless specific approval is obtained from the Sponsor-Investigator Locally advanced tumors at diagnosis, including tumors fixed to the chest wall, peau d'orange, skin ulcerations/nodules, or clinical inflammatory changes (diffuse brawny cutaneous induration with an erysipeloid edge) Patients with a history of previous invasive breast cancer Individuals with a history of a different malignancy are ineligible except for the following circumstances