CCL2 and neoplasm: The CCL2/CCR2 signaling axis is involved in different stages of tumorigenic progression, for example, maintaining the proliferation and stemness of tumor cells at the site of the primary tumor; and when malignant cells metastasize, promoting the invasion of cancer cells into surrounding tissues and circulatory system, and traveling down a specific chemotactic ladder to the site of metastasis (Figure 3).96