The objective of this Phase II study is to assess the diagnostic accuracy of sentinel lymph node (SLN) identification in patients with breast cancer using near-infrared (NIR) fluorescence optical imaging.

Fifty participants consented from Brigham and Women's Hospital (currently enrolling) and Beth Israel Deaconess Medical Center (currently non-enrolling), who will be undergoing standard of care for breast cancer SLN mapping with Tc-99m will be enrolled in this study.

Prior to surgery, patients will undergo lymphoscintigraphy as is standard of care. At the time of SLN mapping, the patient will be injected with indocyanine green dye (ICG). Concurrently, a custom-designed imaging platform that utilizes NIR fluorescence optics will be employed to identify the dye and its path through the lymphatic track, and its eventual highlighting of the SLN. Both color images and NIR images will be merged to give the operating surgeon a clear picture of the ICG track superimposed over anatomical landmarks. This technique will identify the SLN and provide an accurate video image of its location. The surgeon will resect all SLNs identified by Tc-99m or NIR fluorescence, and then confirm the radioactivity and NIR fluorescence signal in each after resection.

Inclusion Criteria:

• Participant must have histologically confirmed breast cancer and be deemed an appropriate surgical candidate with consent for a sentinel lymph node mapping by their oncologic surgeon.
• Age minimum: 18 years.
• Participant must be receiving a planned lymphoscintigraphy procedure.
• Participant must have the ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

• Participants who choose not to proceed with sentinel lymph node biopsy.
• History of allergic reactions attributed to compounds of similar chemical or biologic composition to indocyanine green, including those patients with a history of iodide or seafood allergy.
• Women who are pregnant or may become pregnant, as well as those women who are breastfeeding, will be excluded from this study.