The purpose of this study is to find out if adding radiation therapy to routine medications for breast cancer helps in reducing and preventing the cancer from getting worse. Patients with a locally advanced breast cancer who cannot, or do not want to, undergo surgery are eligible to participate. Participation in this study does not prevent you from undergoing surgery in the future.

Patients who cannot undergo surgical resection for either breast cancer or local control of metastatic cancer have limited effective treatment options. Treatments typically employed in the adjuvant setting have been found in the definitive setting to be inferior to surgery followed by adjuvant therapy. This raises the necessity of evaluating the use of ablative doses of radiation to provide durable local control of the tumor in such patients. Indeed, there is growing evidence that RT is effective in the adjuvant setting. This is a study of concurrent ultra-hypofractionated whole breast whole breast radiation delivered via simultaneous integrated boost to the gross tumor for breast cancer patients not undergoing surgery.

Inclusion Criteria:

• Biopsy proven invasive carcinoma of the breast, either lobular, ductal and/or no special type
• T1-T4, N0-2, M0-1 invasive breast carcinoma by radiological or clinical criteria
• Cancer is deemed unresectable, or the patient is a poor surgical candidate as determined following evaluation by a surgeon, or patient declines surgery.
• Life expectancy > 6 months
• Negative pregnancy test at the time of start of treatment in any female of reproductive age

Exclusion Criteria:

• Concurrent systemic therapy (except for endocrine therapy, HER2-targeted therapy, or immunotherapy which are permitted)
• Prior radiation to ipsilateral breast or regional nodes
• Inability to receive study treatment planning and treatment secondary to body habitus