Background/Aim: Detection of disseminated tumor cells (DTCs) after systemic treatment predicts poor prognosis in breast cancer patients. The aim of our study was to assess the expression of stem-cell marker SOX2 on DTCs and in the primary tumor of patients treated with neoadjuvant chemotherapy (NAT). Materials and Methods: In 170 DTCpositive patients after NAT an additional slide of bone marrow aspirate was stained by double immunofluorescence to detect SOX2-positive DTCs. The SOX2 status of the primary tumor was assessed using the same antibody. Results: The SOX2-status of DTCs was determined in 62 patients and 20 of those (32%) had SOX2 positive DTCs. The SOX2 status of DTCs was not associated with any of the clinicopathological factors. A total of 36% of the patients with a SOX2-negative tumor showed SOX2-positive persistent DTCs. Conclusion: SOX2-positive DTCs can be detected in breast cancer patients after NAT, even in patients with SOX2negative primary tumors. This suggests that these populations may have evolved independently of each other.