CCL2 and neoplasm: Through the HIF-1 pathway, they can secrete PDGF-β, VEGF, angiopoietin-1 (ANG-1), and MCP-1, thereby impairing the function of CD8+ T cells and dampening their anti-tumor effects, ultimately promoting tumor growth and metastasis (Liu et al., 2011; Gibert-Ramos et al., 2021).