STAT3 and breast cancer: Our present study showed that survivin is a downstream effecter of HER2-STAT3 regulation in response to irradiation of HER2-positive breast cancer cells, and that increased STAT3-survivin expression was associated with a poor response to radiotherapy in HER2-positive breast cancers, suggesting that STAT3-survivin is a potential biomarker for radioresistance in HER2-positive breast cancers.