In addition, pan-cancer analysis showed that cytokines (IL-10, TGF-β and CSF-1) and chemokines/ chemokine receptors (CCL18, CCL12, CCL22 and CCR2) participating in immunosuppressive process and co-inhibitory checkpoints (CTLA-4, LAG-3, TIGIT and PDCD1) were all positively correlated with expression of TREM1. Here, CCL18 is linked to cancer.