Tumour-infiltrating microglia and macrophages support glioma progression via multiple mechanisms and make a plausible target in designing new therapeutic strategies.5,7,11,12 Studies with CSF-1R inhibitors in transgenic or experimental murine gliomas point to a role of CSF1 signalling in mediating glioma–microenvironment interactions.16,17 However, CSF1 mRNA levels were not elevated in GBMs in comparison to normal brains or benign astrocytomas.6 Moreover, we found that CSF2 mRNA is elevated in a subset of GBMs, particularly in the mesenchymal GBM subtype being the most aggressive. Here, CSF1R is linked to glioma.