STAT3 and breast cancer: In conclusion, established and novel protein biomarkers of breast cancer including hormone receptors, HER2, uPA/PAI-1, EGFR, pPDGFR, Akt, ERK, PTEN, STAT3 and others, showed considerable intratumoral heterogeneity when assessed by reverse-phase-protein-arrays higher than previously reported for common breast cancer biomarkers [18]–[20].