In the presence of copper (Cu), disulfiram (DSF) suppresses properties associated with cancer stem cells (CSCs) in breast cancer, but the mechanism of action is poorly understood. In the present study, we observed that DSF/Cu treatment induced apoptosis, mediated by caspase-3 activation in triple negative breast cancer (TNBC) cells. DSF/Cu treatment also specifically targeted CSC-like cell populations, marked by the inhibition of ALDH1 activity, the suppression of CD44+/CD24-and CD49f+/CD24 + subpopulations, and the subsequent impairment of mammosphere formation. These effects were functionally associated with a significant impact on the STAT3 signaling pathway, characterized by the downregulation of phospho-STAT3, cyclin D1 and survivin. In an MDA-MB-231-derived xenograft model, DSF administration significantly downregulated ALDH1A1, CD44 and phospho-STAT3 levels. These findings show for the first time that DSF suppresses stem-like properties in TNBC by targeting the STAT3 signaling pathway. (C) 2017 Elsevier Inc. All rights reserved.