The main purpose of this study is to compare genetic markers present on tumor cells before and after chemotherapy.

In this study, the investigators propose that persistent disseminated tumor cells (DTC) present after systemic therapy represent a unique subpopulation of all DTC, are predictors of a poor response to systemic therapy and correlate with poor clinical outcome. The investigators hypothesize that systemic therapy-resistant DTC can be identified by their expression of a unique constellation of tumor marker proteins which may be similar to those expressed by breast cancer stem cells. In this research, the investigators' specific aims are : 1) to characterize tumor markers expressed by DTC which are present after systemic therapy, 2) to compare the expression of these markers to that on DTC detected prior to systemic therapy, 3) to correlate expression of the defined tumor markers on DTC with clinical outcome of breast cancer patients to identify those markers that are predictive of disease recurrence, 4) to utilize biomarkers identified in Specific Aims 1 and 2 to isolate purified DTC for further molecular analysis.

Inclusion Criteria:

• Recently diagnosed with clinical stage II, III, or IV breast cancer
• Planning to undergo neoadjuvant or adjuvant systemic therapy; patients who have already completed neoadjuvant systemic therapy are also eligible
• Must be >= 18 years of age
• If female, must not be pregnant
• Must not have Hepatitis B, C, or HIV
• Must be willing and able to sign informed consent document

Patients seen in clinic at Washington University School of Medicine.