C3AR1 can be expressed by glia, neurons, and infiltrating immune cells in the central nervous system.[43] Recent studies have revealed that a high expression of C3AR1 is positively correlated with a poor prognosis and increased tumor immune infiltration.[44] Four hub genes (C3AR1, TLR3, LY86, TREM2) in yellow module showed moderate positive correlations with the infiltration of immune cells, which may suggest that these 4 genes were upregulated on a variety of tumor-infiltrating immune cells. The gene discussed is TREM2; the disease is neoplasm.