CCL2 and neoplasm: Circulating hypoxia affects the expression of angiogenesis-inducing cytokines such as VEGF-A, CCL2/MCP-1, etc., and recruits various cells into the tumor niche, where they are transformed into tumor-associated macrophages (TAM) involved in tumorigenesis, etc. Through the regulation of transcription factors HIF-1 and NF-κB and their related pathways, regulating the generation of TAMs may be one of the potential tumor-targeted therapeutic options (100).