CCL2 and neoplasm: Single-cell analyses of gallbladder cancer demonstrated that TAM-derived CCL2 engages CCR2 on tumor cells, activating a mitogen-activated protein kinase (MAPK) kinase (MEK)–extracellular signal–regulated kinase (ERK)–ELK1–SNAIL cascade that amplifies epithelial–mesenchymal transition (EMT) and cancer stemness while simultaneously recruiting additional monocytes to reinforce an M2-enriched niche [31].