Levels of MDSC in study patients by pCR or RCB score. Circulating levels of total MDSC (HLADR-, CD33+) were measured by flow cytometry prior to cycle 1 and 2 of anthracycline and cycle 1 and 4 of taxane. Complete pathologic response (pCR) score was determined by a pathologist’s assessment of residual cancer invasive cancer in the breast and lymph nodes. Residual Cancer Burden (RCB) score was determined as follows: RCB 0 - no residual disease, RCB I - minimal residual disease, (RCB score 0–1.35), RCB II - moderate residual disease (RCB score 1.35 – 3.27), RCB III - extensive residual disease (RCB score of >3.28). Patients with RCB classes 0–I were deemed as having complete pathologic response to chemotherapy, while patients with RCB classes II–III were considered not to have achieved good pathologic response. (a–f) Scatter plots for all MDSC measurements from the 24 enrolled patients with central horizontal line indicating mean levels, and error bars representing SD.