Hypofractionated Radiation Therapy After Mastectomy in Preventing Recurrence in Patients With Stage IIa-IIIa Breast Cancer

Inclusion Criteria: * Histologically confirmed invasive carcinoma of the breast of any of the following histologies (ductal, lobular, mammary, medullary, or tubular); patients with metaplastic breast cancer are not eligible * Patients will be staged according to the TNM staging system * For patients not receiving neoadjuvant chemotherapy, pathologic staging must be T0N1-2a, T1N1-2a, T2N1-2a, T3N0-2a, and all M0 status * For patients receiving neoadjuvant chemotherapy, clinical pre-chemo staging and post mastectomy pathological staging is required for all patients; patients who have received neoadjuvant chemotherapy and are pathologically cT0-2 and N0 are only eligible if biopsy-proven clinically N1 or N2 disease is documented prior to the start of neoadjuvant chemotherapy; cT3N0 patients or ypT3N0 patients who receive neoadjuvant chemotherapy may be eligible based on clinical or pathological T stage, and do not require pathologically positive lymph nodes * Note: Higher of the clinical or pathological T and N stage are used for final staging, if receiving neoadjuvant chemotherapy; all patients with clinical, radiographic or pathological T4, N3 or involved internal mammary disease (N1b, N1c, and N2b) are not eligible. N1mic patients are eligible. * No prior therapeutic radiation therapy to the chest, neck or axilla; prior radioactive oral iodine is permitted * No prior history of ipsilateral breast cancer (invasive disease or ductal breast carcinoma in situ \[DCIS\]); l…