Intriguingly, a significant stepwise decrease in the proportion of FABP4+ macrophages (c20) but not other macrophage clusters (i.e., IL1B+, SPP1+, and APOE+) was observed along with adjacent controls, early- and late-stage primary tumors, and brain metastasis of lung cancer26 (all p < 0.001 to normal tissue) (Fig. 1g and Supplementary Fig. S1e), suggesting that FABP4+ macrophages may negatively correlate with lung cancer progression. Here, APOE is linked to lung cancer.