For instance, in brain tumors, by using CCR2-KO to reduce monocyte migration toward tumors, it was noted that the microglia population increased.64 Conversely, when microglia are depleted, monocytes fill the microglia’s ecological niche and adopt related phenotypic traits.65 The characteristics of TAMs in the TME are determined by the cell’s genetic background, the tumor microenvironment, and the tissue environment.16 This suggests a potential for MDMs and TRMs to transform into each other. The gene discussed is CCR2; the disease is neoplasm.