In this study, we demonstrate that different breast cancer cell lines after treatment with clinically relevant concentrations of 5-fluorouracil, doxorubicin, or paclitaxel enrich CSCs, increase expression of IL-6, IL-8, and MCP-1 cytokines, and up-regulate activation of NF-κB and Stat3 pathways. This evidence concerns the gene STAT3 and breast carcinoma.