This is a nested multicenter, prospective cohort study within the I-SPY 2 TRIAL for women undergoing neoadjuvant chemotherapy for primary breast cancer who are also undergoing definitive surgical resection and have clinical or radiographic evidence of residual tumor at the completion of chemotherapy.

Inclusion Criteria:

• Enrollment on the treatment phase of the I-SPY 2 TRIAL
• Completed a standard neoadjuvant chemotherapy regimen or assigned treatment on I-SPY 2 and planning definitive surgical resection. Participants who have discontinued assigned treatment on I-SPY 2, switched to standard of care, and have completed a standard neoadjuvant chemotherapy regimen are still considered eligible.
• Pre-surgical imaging or clinical examination demonstrating residual disease in the breast. Participants with any extent of enhancement attributable to tumor on the pre-surgical MRI are eligible. No minimum extent of palpable tumor pre-surgery is required.
• Willing to undergo bone marrow aspiration and blood specimen collection per protocol specifications
• No clinical evidence of distant metastatic disease. Pre-chemotherapy staging scans are sufficient in the absence of any symptoms or subsequent clinical evidence suggesting distant metastases
• Age 18 or over and are able to give informed consent

Exclusion Criteria:

• Individuals under the age of 18
• Individuals who cannot understand and give informed consent. We will not be assessing decisional capacity; determination of ability to give informed consent will be at the discretion of the treating physician.
• Pregnancy. Participants in the parent I-SPY 2 TRIAL are screened for pregnancy at enrollment and pregnancy is an exclusion criteria. No additional screening for pregnancy is required for participants enrolling on SURMOUNT. However if a study participant does become pregnant while on study or during the course of the 10 year follow-up, the study participant will remain on the study protocol and will not be withdrawn. Because this is an observational study and does not have a therapeutic component, there will be no increased risk to following a study participant through annual blood draws and medical information abstraction from the medical chart who may or may not become pregnant during the course of the follow-up period.

women undergoing neoadjuvant chemotherapy for primary breast cancer who are undergoing definitive surgical resection and have clinical or radiographic evidence of residual tumor at the completion of chemotherapy