Comparing the percentage of GPNMB expressing TAMs to CD45+CD11b+Ly6G−Ly6c− cells in naïve brain representing microglia (naïve brain = 7.98% ± 2.37 SD vs. tumor brain = 43.2% ± 18.09 SD; p = 0.0028) and naïve spleen representing macrophages (naïve spleen = 8.98% ± 1.7 SD vs. tumor brain = 43.2% ± 18.09 SD; p = 0.0034), we found significantly higher GPNMB levels in TAMs, indicating that the TME induces an upregulation of GPNMB expression in TAMs. This evidence concerns the gene PTPRC and brain neoplasm.