In line with a recent report that CXCL9 and SPP1 indicate tumor-associated macrophage polarity in human cancers [23], Cxcl9 expression was significantly higher in Trem2− macrophages, whereas Spp1 expression was significantly upregulated in Trem2+ macrophages (Supplementary Fig. 2C). Here, TREM2 is linked to cancer.