CCL17 and neoplasm: Tumor associated macrophages (TAMs) and myeloid suppressor cells (MDSCs) release chemokines, such as CCL17, CCL22, CCL5, CCL6 or CCL28, depending on the tumor type, to attract Tregs expressing the chemokine receptors CCR4, CCR5, CCR10 and CXCR3 from secondary lymphoid tissues to the tumor [24].