Intraoperative Radiation Therapy in Treating Patients With Breast Cancer Undergoing Breast-Conserving Surgery

Inclusion Criteria: * Suitable for breast conserving surgery * T1 and T2 (\< 3.5 cm), N0, M0 Exclusion Criteria: * Axillary lymph node positive breast cancer * Tumor size \> 3.5 cm * Extensive intraductal component (EIC \>= 25% of the lumpectomy specimen involved with ductal carcinoma in situ), as assessed on surgical pathologic lumpectomy specimen * Multicentric cancer in the same breast as diagnosed by clinical examination, mammography, ultrasound; magnetic resonance imaging (MRI) or pathologic assessment, not amenable to excision with negative margins with a single lumpectomy * Inability to assess pathologic margin status * Synchronous bilateral breast cancer at the time of diagnosis * Ipsilateral breast had a previous cancer and/or prior in-field radiation * Patients known to have BRCA1/2 gene mutations (testing for gene mutations is not required) * Patients undergoing primary systemic treatment (hormones or chemotherapy) as initial treatment with neoadjuvant reducing tumor size * Previous history of malignant disease does not preclude entry if the expectation of relapse-free survival at 10 years or greater * Any factor included as exclusion criteria in the participating center's treatment policy statement * Additional exclusion criteria for University of California San Francisco (UCSF) (as laid out in the Treatment Policy): * Patients under the age of 50 * Estrogen receptor negative (as defined in Treatment Policy under "Pathology") * Human epidermal growth fac…