Taken together, the interleukin-6 (IL-6) and the signal transducer and activator of transcription 3 (STAT3) or IL-6/STAT3 pathway is a central regulator of breast cancer metastasis by promoting breast cancer cell proliferation, the development of metastasis (by the epithelial–mesenchymal transition (EMT) and enriching cancer stem cells (CSCs)), and suppressing apoptosis. This evidence concerns the gene STAT3 and breast cancer.