STAT3 and lung cancer: Furthermore, only the expression of PPAR-γ and Arg1 but not other key transcription factors such as STAT1, STAT3 and C/EBPβ was dramatically reduced in Ffar2−/− MDSCs (Fig. 6F and G, and Additional file 1: Fig. S8C and D) and urethane-induced lung cancer tissues (Additional file 1: Fig. S8E).