Radiation Therapy for ypN0 Breast Cancer

Inclusion Criteria: * WHO performance status 0-1 * Invasive Breast Cancer with cT1-3 cN1-2 at time of diagnosis * Axillary nodal involvement can be detected using, clinical examination, ultrasound, CT scan or PET scan * Pathologic confirmation using, FNAC, core biopsy or excisional biopsy * ER, PR, Her2 neu and Ki67 status should be available for all patients * All patients should have received standard preoperative chemotherapy prior to surgery * At the time of surgery, all patients should have axillary clearance with at least 6 nodes harvested from the axilla * Patients who have undergone mastectomy or lumpectomy with negative margins with ypN0, ypN0(+i) or ypN0(+mol) are eligible for randomization Exclusion Criteria: * Poor performance status * Definitive clinical or radiologic evidence of metastatic disease * T4 tumors including inflammatory breast cancer * N3 disease detected clinically or by imaging * Patients with histologically positive axillary nodes after preoperative chemotherapy * Positive surgical margin after definitive surgery * Previous ipsilateral or contralateral breast cancer * Previous chest wall or breast irradiation * Second primary cancer * Active connective tissue disease