CSF2 and cancer: A positive feedback loop of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) and the chemokine CCL18 has also been demonstrated: CCL18 secreted by TAMs primes cancer cells into a mesenchymal-like phenotype, and in turn, these cancer cells upregulate the expression of GM-CSF as a differentiation activator of monocytes into TAMs (113).