STAT3 and cancer: Furthermore, miR-21 in oral squamous cell carcinoma (OSCC) enhanced the immunosuppressive function of MDSCs through an miR-21/PTEN/PD-L1 axis (69) and in esophageal squamous cell carcinoma (ESCC), miR-21 activated the STAT3 pathway carried by cancer-associated fibroblast (CAF)-secreting exosomes, which upregulated the induction of M-MDSC corporate with IL-6 (70).