Background: Neoadjuvant chemotherapy (NAC) for breast cancer (BC) is being increasingly used in patients with stage I/II disease. Although previously reserved for patients with locally advanced disease, its use in patients with localized disease allows for higher rates of breast-conserving procedures and provides insight into tumor biology. A complete pathologic response (pCR) to NAC correlates with better clinical outcomes; sadly, many patients do not achieve pCR. The advent of immunotherapy has provided cancer patients with additional treatment options. To optimize immunotherapy in BC we must understand the peripheral cellular immunome (immune subsets and activation status) of patients as they undergo standard of care therapy (SOC). Methods: Our population includes patients with stages I-III BC undergoing SOC. Samples were collected pre- and post-NAC, post-surgery and at 2-month follow-up (FU). Results: Flow cytometry analysis for 11 patients was performed at each time-point to examine percentages of circulating immune cells (see Table). We grouped samples in 3 categories: human epidermal growth factor receptor 2 (HER2+) positive, HER2 negative (HER2-) and triple-negative (TN) tumors. 3 out of 11 patients had pCR (1 HER2+, 1 HER2-, 1 TN); they had highest percentage of circulating CD56+ NK cells during treatment course. Conclusions: We observed striking changes in the immunome of women with stage I-III BC undergoing NAC. Although our findings are preliminary, given our sample size, we observed distinct trends within each immune cell population in specific tumor receptor subtypes. These trends could serve to guide our therapies, allow for better patient selection and predict treatment response in patients.