The purpose of this study is to provide prospective evidence in the US population of the frequency of skin discoloration and Sentinel Lymph Node detection rate in patients who have recevied Magtrace for Sentinel Lymph Node Biopsy (SLNB) and to evaluate the impact that skin discoloration has on patients when it does occur using patient reported outcome measures.

The purpose of this study is to provide prospective evidence in the US population of the frequency of skin discoloration and Sentinel Lymph Node (SLN) detection rate in patients who have received 1ml Magtrace for Sentinel Lymph Node Biopsy (SLNB) and to evaluate the impact that skin discoloration has on patients when it does occur using patient reported outcome measures utilising BREAST-Q.

Baseline assessment using BREAST-Q will performed. A key secondary objective is to demonstrate non-inferiority of sentinel lymph node (SLN) detection rate with Magtrace compared to the American Society of Breast Surgeons (ASBRS) performance standards.

All participants will undergo lymph node mapping with Magtrace, and Sentinel Lymph Node Biopsy undertaken and nodes localised with the Sentimag system, A sentimag count will be recorded for each node removed.

After completion of the surgery, at the postoperative visit the presence of Magtrace related discoloration will be assessed by the Investigator. Participants found to have no Magtrace related discoloration will be asked to complete the Post-Op BREAST-Q assessment and return at 12 months post-op for a follow-up visit. Those patients assessed as having the presence of Magtrace related skin discoloration will be asked complete the post-op BREAST-Q and will then undergo assessment of the size and severity of the discoloration. They will then be asked to return at 6, 12, 18 and 24 months for follow-up visits, or until the discoloration has resolved. At each of these visits the BREAST-Q will be completed, and the size and severity assessment will be performed.

Inclusion Criteria:

• Patient is willing and able to give informed consent for participation in the study
• Patient is aged 18 years or older at the time of consent
• Patients undergoing planned breast conserving surgery (for example, lumpectomy or partial mastectomy) and SLNB with Magtrace

Exclusion Criteria:

• The patient is pregnant or lactating
• The patient has had prior breast radiation to the ipsilateral breast
• The patient has clinical or radiological evidence of metastatic cancer including palpably abnormal or enlarged lymph nodes
• The patient has recevied a Feraheme (ferumoxytol) injection within the past 6 months
• The patient has intolerance or hypersensitivity to iron or dextran compounds or to Magtrace
• The patient has iron overload disease
• The patient has discoloration on the breast (such as tattoo, birthmark, tanning, rash etc.), that in the Investigator's opinion, could impact the clinical trial results, specifically the assessment of any skin discoloration, or plans to have a tattoo on the breast post-operatively.

Subjects considered for enrollment will be at least 18 years old at the time of consent, and: a) due to undergo planned breast conserving surgery (for example lumpectomy or partial mastectomy) and SLNB with Magtrace b) meet all other inclusion and no exclusion criteria