CCL2 and neoplasm: Diferentiation trajectory analysis of macrophages showed the transformation of M1 to M2 macrophages during osteosarcoma progression (Figure 1H), which was further supported by analyzing the relationship between the expression levels of the top 30 M1 and M2 macrophages or M2 polarization genes such as CCL2, CXCR4, IL10, MAF, and STAT3 and tumor progression (Figure 1I-J).