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): 40.0-99.0,  DCIS Ductal Carcinoma in Situ Diagnosis of unilateral, bilateral, unifocal, multifocal, or multicentric DCIS without invasive breast cancer (date of diagnosis defined as the date of the first pathology report that diagnosed the patient with DCIS) OR: atypia verging on DCIS OR: DCIS + LCIS (mix and/or separate locations in the same breast) A patient who has had a lumpectomy or partial mastectomy with margins positive for DCIS (i.e. <2mm/ink on tumor) as part of their treatment for a current DCIS diagnosis is also eligible (post-excision bilateral mammogram required at enrollment to establish a new baseline) No previous DCIS or invasive breast cancer in ipsilateral breast 5 years prior to current DCIS diagnosis years of age or older at time of DCIS diagnosis ECOG performance status 0 or 1 No contraindication for surgery Baseline imaging (must dimensions) Unilateral DCIS: contralateral normal mammogram ≤ 6 months of registration and ipsilateral breast imaging ≤ 120 days of registration (must ipsilateral mammogram; can also ultrasound or breast MRI) Bilateral DCIS: bilateral breast imaging ≤ 120 days of registration (must bilateral mammogram; can also ultrasound or breast MRI) DCIS s/p lumpectomy: post excision mammogram on side of excision ≤ 60 days of registration  Male DCIS Grade III DCIS Concurrent diagnosis of invasive or microinvasive breast cancer in either breast Documented mass on examination or mass/hypoechoic area on imaging at site of DCIS prior to biopsy yielding diagnosis of DCIS, with exception of: subsequent lumpectomy or partial mastectomy (with positive DCIS margins i.e. <2mm/ink on tumor) followed by a post-surgery MMG; fibroadenoma at a distinct/separate site from site of DCIS; or diagnosis of mass/hypoechoic area as a cyst or a papilloma. In cases of uncertainty about whether the mass was present on physical examination prior to biopsy, the following should be applied: if mammogram noting abnormal findings is diagnostic MMG = symptomatic/if mammogram noting abnormal findings is screening MMG = asymptomatic. If a patient has a mass on imaging that is biopsied (worked-up) and does not show invasive breast cancer, they are eligible. If a patient has a mass on initial MMG that is not seen on subsequent MMG, they are eligible (if initial mass occurred due to additional work-up) Any color/bloody nipple discharge (ipsilateral breast) Mammographic finding of 4 or greater within 6 months prior to registration at site of breast other than that of known DCIS, without pathologic assessment Use of investigational cancer agents within 6 weeks prior to diagnosis of DCIS Any serious and/or unstable pre-existing medical, psychiatric, or other existing condition that would prevent compliance with the trial or consent process Pregnancy. If a woman has been confirmed as pregnant, she will not be eligible to take part in the trial. If she suspects there is a chance that she may be pregnant, a pregnancy test should be undertaken, although a pregnancy test for all women of child-bearing potential is not mandatory. In addition, if a woman becomes pregnant once registered to the trial, she can continue to be followed (endocrine therapy is not a mandatory requirement of the study) Documented history of prior tamoxifen, aromatase inhibitor, or raloxifene use in the 6 months prior to registration