One plausible hypothesis warranting future investigation regards the upregulation of glutamine synthetase (GS), which was identified in TAMs sorted from mice Lewis lung carcinoma (LLC) tumors [16], as well as in human TAMs isolated from glioblastoma tissues [61], and which was found to be intimately associated with pro-tumoral TAM polarization [62]. This evidence concerns the gene GLUL and glioblastoma.