ISG15 and cancer: A subpopulation unregulated(S100A9+_Microglia: S100A8 and S100A9), an immune regulatory microglia(GPNMB+_Microglia: GPNMB and CD9), formerly reported as TAM promoting cancer metastasis and stemness in macrophage (14), a chemokinase microglia subtype(CCL3L1+_Microglia:CCL4 and CCL3L1 etc.), an ISG microglia cluster(ISG15+_Microglia:ISG15,IFI6 and IFI44L), a precursor-like microglia(PTN+_ Microglia: PTN, PTPRZ1 and SOX2), secreting PTN to significantly promote tumor invasion (15) and a subgroup(CACNA1A+_Microglia) highly expressed CACNA1A with unclear function.