CCL2 and esophageal squamous cell carcinoma: Another mechanism that the increased CD163+ TAM in the TME promote ESCC tumor progression is that they can augment angiogenesis by releasing thymidine phosphorylase (TP) under the influence of macrophage chemotactic protein-1(MCP-1) (45, 46), inducing vascular endothelial growth factor (VEGF) expression in EC cells (45, 47), and promoting stromal cell matrix metalloproteinase 9 (MMP9) production (48).