The purpose of this study is to investigate the use of intra-operative Magnetic Resonance Imaging (MRI) and Mass Spectrometry (MS) during breast conserving surgery, and to determine if these tests are capable of accurately predicting the presence or absence of breast tumor in surgical specimens at the margins.

This research study is a Phase II clinical trial investigating the use of intra-operative MRI and MS in breast cancer surgery. Phase II clinical trials test the safety and effectiveness of an investigational intervention to learn whether the intervention works in treating a specific disease. "Investigational" means that the intervention is being studied.

Prior research has shown that intraoperative MRI and MS are two types of tests that are feasible to use during cancer surgery and may be able to guide therapy. In this study, we are evaluating the accuracy of intra-operative MRI and MS in determining whether or not all cancer tissue was removed during breast surgery.

Inclusion Criteria:

• Patients must be female
• Participants must have a pre-operative standard mammogram with or without ultrasound. These may be performed at outside institutions.
• Participants must have biopsy confirmed and clinical stage 1 or stage 2 breast carcinoma. If biopsy was done at an outside hospital, pathology will be reviewed at BWH/DFCI.
• Participants must be candidates for definitive local therapy with breast conserving therapy (this takes into account tumor to breast size ratio appropriate for BCS, and the ability to undergo standard radiation therapy post-operatively).
• Patient must meet standard MRI guidelines and be able and willing to undergo MRI
• Age ≥18 years and < 75.
• Ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

• Participants with a known BRCA 1 or 2 mutation.
• Participants with known Li-Fraumeni or Cowden's Disease.
• Participants with prior mantle radiation.
• Participants with locally advanced breast cancer such as inflammatory breast cancer or cancer grossly involving skin.
• Participants who are pregnant.
• Participants who enroll in a preoperative therapy trial or who have been treated with neoadjuvant chemotherapy.
• Participants with known active collagen vascular disease.
• Participants with prior history of ipsilateral breast carcinoma.
• Patients who have biopsy confirmed multi-centric disease.
• Participants who have documented contra-indications for contrast-enhanced MRI, including but not limited to renal failure.
• Participants who exceed the weight limit for the surgical table at AMIGO, 350 lbs or who will not fit into the 70 cm diameter bore of the MRI scanner at AMIGO or the 60 cm diameter bore of the pre-procedure imaging MRI scanner.