Brain tumors exhibit significantly higher levels of TREM2 expression, predominantly in tumor-associated myeloid cells. (A) Top 6 types of tumors with elevated TREM2 expression in a descending order from left to right, which were glioblastoma (GBM), brain lower grade glioma (LGG), kidney renal clear cell carcinoma (KIRC), kidney renal papillary cell carcinoma (KIRP), pancreatic adenocarcinoma (PAAD), and breast cancer (BRCA). (B) UMAP plots displaying the immune cells in patients with newly diagnosed GBM. (C, D) TREM2 transcription in different immune cell populations. (E) TREM2 is not detected in brain tumor cells. The data were shown as mean ± SEM and analyzed by 1-way ANOVA. (F) The correlation between TREM2 expression and signature genes related to myeloid cell phagocytosis, immunosuppression, and antigen presentation was evaluated in LGG and GBM patients. The Spearman’s correlation test produces both P-values and correlation coefficients (R²). All listed genes had a P-value of less than 0.05. Genes with an R² value greater than 0.25 were considered to have a correlation (either positive or negative) with TREM2 expression.