STAT3 and breast cancer: In stem cells and breast cancer, the activity of the Notch signalling pathway is critical for activation of signal transducer and activator of transcription 3 (STAT3).22, 23 STAT3 activation is not only associated with increases in malignant cancer behaviours (uncontrolled growth, migration, invasion and therapeutic resistance),24, 25 it may also exert a critical influence on establishing cell polarity during directed cancer cell progression, processes significant for EMT programmes.26