The aim of this study was to explore the red blood cell changes that occur during neoadjuvant dose-dense chemotherapy (NAC) of breast cancer. Also, we investigated the role of macrocytosis as a predictive biomarker for pathological complete response and disease-free survival (DFS) in these patients. A retrospective analysis of 82 breast cancer patients' data treated with anthracycline-cyclophosphamide-paclitaxel (AC-T) NAC in three oncology institutions in south Croatia from 2013 to 2020 was carried out. During chemotherapy mean corpuscular volume increased with time, with a median increase of 7.25 fl. Macrocytosis was induced in 38% of patients overall. Development of macrocytosis did not correlate with DFS hazard ratio = 0.525; 95% confidence interval (CI), 0.074-3.768; P = 0.525. Higher percentage of patients in macrocytosis group achieved PCR, 39% vs. 29% in no macrocytosis group, but this difference was not statistically significant. The relevance of macrocytosis induction during dose-dense neoadjuvant chemotherapy in breast cancer should be further explored.