SABER Study for Selected Early Stage Breast Cancer

Who May Qualify: 1. Female, ≥ 50 years of age. 2. Oncotype or MammaPrint diagnosis results are required prior to the start of treatment 3. diagnosed by tissue sample (biopsy-confirmed) invasive breast cancer. 4. Clinical stage T1N0M0. 5. Receptor status: Estrogen-Receptor (ER)/Progesterone-Receptor (PR) positive and Human Epidermal Growth Factor Receptor 2 (HER2) negative. 6. Unifocal breast cancer. 7. Eastern Cooperative Oncology Group (ECOG) 0, 1. 8. Ability to undergo MRI. 9. Women of child-bearing potential (WOCBP) must agree to use adequate contraception or agree to undergo sexual abstinence prior to study entry and for the duration of study participation. WOCBP must have a negative serum or urine pregnancy test at time of enrollment. Should a woman become pregnant or suspect she is pregnant while she is participating in this study, she should inform her treating physician immediately. 10. Ability to understand the investigational nature, potential risks and benefits of the research study and willingness to sign the written willing to sign a consent form and HIPAA document(s). Who Should NOT Join This Trial: 1. Patients without diagnosed by tissue sample (biopsy-confirmed) invasive breast cancer. 2. Patients without Oncotype or MammaPrint diagnosis results at the start of treatment. 3. Patients with metastatic disease. 4. ECOG 2, 3, 4. 5. Patients that are unable to undergo MRI. 6. Prior history of radiation to the chest. 7. History of collagenous disease (systemic lupus erythematosus, scleroderma, dermatomyositis). 8. Any serious medical or psychiatric illness/condition likely in the judgment of the Investigator(s) to interfere or limit compliance with study requirements/treatment. 9. Diagnosis of another primary malignancy within the last 5 years with the exception of non-melanoma skin cancer. 10. Patients unable to consent, who are pregnant or nursing, or are prisoners. Always talk to your doctor about whether this trial is right for you.