USP21 and esophageal cancer: Our observations are in line with previous studies that linked USP21 with the STAT3 phosphorylation level, suggesting the role of USP21 in the regulation of activation of STAT3/FOXO1 pathway and glycolysis in esophageal cancer cells (45) and STAT3/FOXD1 in a process of self-renewal of mesenchymal glioblastoma stem cells (46).