STAT3 and breast cancer: Additionally, the pro-inflammatory proteins S100A8 and S100A9 are upregulated by STAT3 and have a role in the expansion of MDSC in tumours by preventing myeloid-cell differentiation and in abrogating T-cell function in breast cancer, ovarian cancer and gastric cancer (Arai et al. 2008, Sinha et al. 2008, Wang et al. 2013).