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,  Invasive Breast Carcinoma Stage II Breast Cancer Stage IIA Breast Cancer Stage IIB Breast Cancer Stage IIIA Breast Cancer The patient must have signed and dated an Institutional Review Board (IRB)-approved consent form that conforms to federal and institutional guidelines The patient must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 Patients must have had ER analysis performed on the primary breast tumor collected prior to neoadjuvant therapy according to current American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guideline recommendations for hormone receptor testing; if negative for ER, assessment of progesterone receptor (PgR) must also be performed according to current ASCO/CAP Guideline Recommendations for hormone receptor testing. Patients who have a primary tumor that is hormone receptor-positive or hormone receptor-negative are eligible Patients must have had HER2 testing performed on the primary breast tumor collected prior to neoadjuvant chemotherapy according to the current ASCO/CAP guideline recommendations for human epidermal growth factor receptor 2 testing in breast cancer; patients who have a primary tumor that is HER2-positive, HER2-equivocal, or HER2-negative are eligible Patients must have had a biopsy marker placed within the tumor bed with imaging confirmation (preferably mammogram but ultrasound or magnetic resonance imaging [MRI] is acceptable) of marker placement prior to neoadjuvant chemotherapy Patients with operable focal or multifocal (T1-T3, stage II or III invasive ductal carcinoma [all receptor phenotypes]), and who have completed neoadjuvant chemotherapy with a clinical complete response (by clinical examination) Patients with synchronous bilateral breast cancer are eligible if at least one of the synchronous breast cancers has a cCR, and the side with a cCR meets criteria. (Patients with previous contralateral invasive breast cancer treated with anti-cancer therapy are eligible.) Patients must have achieved a complete or near complete radiologic tumor response on breast imaging with mammogram, ultrasound, and MRI during or after completion of appropriate neoadjuvant chemotherapy defined as Mammogram with malignant appearing calcification or mass ≤ 1 cm; or Ultrasound with a hypoechoic area ≤ 2 cm; or  T4 tumors including inflammatory breast cancer Patients with distant metastatic disease Lumpectomy performed prior to study entry Patients with any history of prior radiation therapy in the affected breast Patients with a prior history of ipsilateral invasive breast cancer; (patients with previous ipsilateral/contralateral DCIS or previous contralateral invasive breast cancer treated with anti-cancer therapy are eligible) Patients with invasive lobular carcinoma Patients who have multicentric disease Patients treated with neoadjuvant hormonal therapy only are not eligible Patients who are medically unfit to undergo surgical resection Patients without breast biopsy marker documented by imaging at tumor bed site prior to initiation of neoadjuvant therapy