Macrophages can boost the release of tumor‐promoting cytokines and immunosuppressive cytokines, including PGE2, VEGF, MCP‐1, IL‐6, IL‐1β, MMP‐9, TNF‐α, and cytidine deaminase (CDA), to enhance the pre‐metastatic fibrotic microenvironment, promote tumor cell proliferation, migration, invasion and EMT, and enhance tumor cell resistance,239, 240, 241, 242 and can express programmed death ligand‐1 (PD‐L1), bind to PD‐1 on T cells, deliver immunosuppressive signals and suppress immune effector T cells.243, 244. The gene discussed is MMP9; the disease is neoplasm.