PMN-MDSCs differentiate from granulocyte–monocyte progenitors (GMPs) and granulocyte progenitors (GPs) in the bone marrow (BM) through the binding of C–C motif chemokine ligand 20 (CCL20), which is expressed at high levels in BC cells, to its receptor CCR6 [124]. The gene discussed is CCL20; the disease is breast cancer.