STAT3 and cancer: Constitutive STAT3 expression induces neoplastic transformation and tumorigenesis, driving cancer development, maintenance of stemness and promotion of tumorigenicity.1, 5 A major component of STAT3 activity is its multifaceted promotion of immune suppression, which includes activation of myeloid-derived suppressor cell (MDSC) function and tumour-supportive macrophage polarisation.