CCL2 and cancer: Moreover, monocytes release monocyte chemo-attractant protein-1 (MCP-1) upon stimulation and mediate tumor-associated macrophage infiltration in solid tumors, which have been shown to produce a variety of chemokines, such as transforming growth factor-α (TGF-α), TNF-α, IL-1, and IL-6, to promote tumorigenesis, angiogenesis, and distant metastasis of malignant tumors [34, 35].