Histopathological and single-cell profiling studies demonstrate that up to one-third of tumour cellularity can comprise glioma-associated microglia and bone-marrow-derived macrophages, which adopt tumour-supportive phenotypes characterised by STAT3 activation, immunoregulatory cytokine secretion and impaired antigen presentation (10, 11). Here, STAT3 is linked to central nervous system cancer.