Accordingly, normal cells with over-activated STAT3 gain the features of tumour cells.5,10 Reciprocally, elimination of STAT3 efficiently inhibits tumorigenesis and tumour cell growth in colon cancers.17 In addition, the expression and activation of STAT3 correlate with tumour grade, stage, the appearance of metastases and recurrence in breast cancers.18 To date, various STAT3 inhibitors have been developed for the therapy of different cancers.19–21 However, effective therapeutic strategies for inhibiting STAT3 remain to be further developed.22 This evidence concerns the gene STAT3 and breast cancer.