This study seeks to enroll women with breast cancer undergoing neoadjuvant chemotherapy to evaluate if Diffuse Optical Spectroscopy Imaging (DOSI) can predict a patient response to chemotherapy treatment. DOSI is a noninvasive imaging method that uses harmless near-infrared light using simple wearable probes held against the skin by transparent dressings to predict tumor metabolic activity. It uses nonionizing radiation, requires no external contrast agent and uses low light exposure to human tissue. DOSI scans can be performed frequently at the bedside in settings such as a doctor's office or infusion center.

DOSI has already shown promise in monitoring breast cancer patients undergoing preoperative chemotherapy. Several groups have demonstrated optical changes predictive of response in the course of weeks to months of treatment. The investigators group has begun to show that DOSI measurements during drug infusions and at early time-points (first 24 hours) correlate with tumor final pathological response. While this data is provocative, significantly more work is needed to confirm that early time-points are predictive in different treatment groups and tumor molecular subtypes.

In this study, breast cancer patients will receive DOSI scans at a subset or all of the following time-points: baseline, during drug infusion, early therapy, mid-therapy and post-therapy. DOSI results will be compared to standard of care pathology results determined after surgery. Additionally, the investigators will correlate DOSI parameters with any additional biopsy specimens taken during treatment (typically for patients on adaptive treatment trials). Each DOSI scan will take about 30-60 minutes/ session, although infusion measurements will take longer. DOSI can potentially help doctors to gain information necessary to make evidence-based changes in treatment strategies of individual patients. The investigators long-term goal is to provide oncologists with a relatively simple, risk-free bedside tool that can help predict response early, thereby maximizing therapeutic response and minimizing unnecessary toxicity.

A cohort of 10 additional patients with breast cancer who are not receiving neoadjuvant chemotherapy (NAC) who will only be measured at baseline has been created. Complete characterization of baseline properties in patients is essential for understanding subsequent changes from baseline in response to chemotherapy. Adding an additional 10 patients who are not receiving NAC to be enrolled will allow for better characterization of baseline properties, which in turn will allow for a better understanding of the changes in properties seen in those patients who are undergoing NAC.

Inclusion Criteria for Neoadjuvant Chemo (NAC) Cohort:

1. Female;
2. Diagnosis of invasive breast cancer by clinical breast examination, by standard of care diagnostic imaging, or by initial tissue biopsy;
3. Planned for primary systemic (neoadjuvant) chemotherapy and surgical resection of residual primary tumor following completion of neoadjuvant chemotherapy;
4. Tumor size ≥ 2cm, measured on imaging or estimated by physical exam;
5. Planned definitive breast surgery (mastectomy or lumpectomy/breast conservation) following completion of neoadjuvant therapy;
6. Age 18 years or older;
7. Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 2 (Karnofsky performance status ≥ 60%;
8. Adequate organ and marrow function, as defined at Boston Medical Center (BMC);
9. Postmenopausal for a minimum of one year, OR surgically sterile, OR not pregnant, confirmed by a pregnancy test as per institutional standard of care, and willing to use adequate contraception (hormonal or barrier method of birth control; abstinence) for the duration of study participation;
10. Able to understand and willing to sign a written informed consent document and a Health Insurance Portability and Accountability Act (HIPAA) authorization in accordance with institutional guidelines.

Inclusion Criteria for Non-NAC Cohort:

1. Female;
2. Diagnosis of invasive breast cancer by clinical breast examination, by standard of care diagnostic imaging, or by initial tissue biopsy;
3. Tumor size ≥2cm, measured on imaging or estimated by physical exam;
4. Planned definitive breast surgery (mastectomy or lumpectomy/breast conservation) following completion of neoadjuvant therapy;
5. Age 18 years or older;
6. ECOG Performance Status ≤ 2 (Karnofsky performance status ≥ 60%; see Appendix II);
7. Adequate organ and marrow function, as defined at BMC;
8. Postmenopausal for a minimum of one year, OR surgically sterile, OR not pregnant, confirmed by a pregnancy test as per institutional standard of care, and willing to use adequate contraception (hormonal or barrier method of birth control; abstinence) for the duration of study participation;
9. Able to understand and willing to sign a written informed consent document and a HIPAA authorization in accordance with institutional guidelines.

Exclusion Criteria for All Cohorts:

1. Previous treatment (chemotherapy, radiation, or surgery) to involved breast;
2. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements;
3. Medically unstable;
4. Under age 18;
5. Pregnant or nursing;
6. Previous malignancy, other than basal cell or squamous cell carcinoma of the skin or in situ carcinoma of the cervix, from which the patient has been disease free for less than 5 years;
7. No contraindications for primary chemotherapy.

The first cohort will consist of participants with up to 9 DOSI scans at 6 different time points during the course of their neoadjuvant chemotherapy (NAC). The time course of chemotherapy may vary between 3-9 months depending on the type chemotherapy subjects receive.

There will be a second cohort of patients with breast cancer who are not receiving neoadjuvant chemotherapy (NAC) and who will only be measured at baseline.