Once Tregs reach the tumor, differentiation/polarization and activation is induced by a variety of tumor- and immune-derived factors, including TGFβ [113,152,153,294], IL-10 [301,302], PGE2/COX2 [112,113,155], IL-35 [301,302], adenosine [222,223,315], IL-6/STAT3 [334], and even has_circ_0069313, a tumor-derived circular RNA that helps Tregs maintain FoxP3 levels [335]. This evidence concerns the gene PTGS2 and neoplasm.