Breast-Conserving Surgery Followed by Radiation Therapy With MRI-Detected Stage I or Stage II Breast Cancer

Inclusion * Patients with multicentric carcinoma (tumors in different quadrants of the breast or tumors separated by at least 4 cm) * All radiographically suspicious lesions must be biopsied and have histologically confirmed ductal carcinoma in-situ, invasive ductal, invasive lobular, medullary, papillary, colloid (mucinous), or tubular histologies * A maximum of two radiographically detected malignant lesions * Clinical Stage I-II breast carcinoma, with lesion size =\< 5 cm for the dominant mass and the second lesion detected only on MRI, treated with lumpectomies; the MRI detected lesion must be pathologically =\< 1 cm * Axillary lymph node evaluation, either sentinel lymph node biopsy or axillary dissection as deemed appropriate by the treating surgeon for all patients with invasive cancer; no axillary lymph node sampling is needed for patients with DCIS * Negative resection margins with at least a 2 mm margin from invasive and in-situ cancer or a negative re-excision * A posterior margin =\< 2 mm from DCIS is permissible provided fascia was taken * Patients are eligible regardless of estrogen receptor, progesterone receptor, or Her-2/neu amplification * Hormonal therapy is allowed; if adjuvant chemotherapy is planned, the chemotherapy should be delivered first and radiation must begin no earlier than three weeks and no later than eight weeks following completion of chemotherapy * Signed study-specific informed consent prior to study entry Exclusion * Extensive intraduc…