STAT3 and neoplasm: In mixed leukemia, tumor-secreted factors GM-CSF/IL-6 upregulate high expression levels of miR-21a/21b/181b through STAT3/CEBPβ pathway, further diminishing the expression of WD repeat-containing protein 5 (Wdr5), absent small or homeotic-like (ASH2L) and mixed lineage leukemia 1 (MLL1), which are involved in the expansion and differentiation of G-MDSC.