In conclusion, the expression and mechanism of STAT3, HIF, NF-κB, metabolic pathways, pattern recognition receptors, etc. will recruit MDSCs, increase the expression levels of Arg1, INOS, PD-L1, make them accumulate and expand rapidly in the tumor microenvironment, increase their immunosuppressive function as well as inhibit the role of CD8 + T, thus promote tumor progression. Here, NOS2 is linked to neoplasm.