CCL17 and neoplasm: In skin cancer, chemokines such as CCL-17 and CCL-18 secreted by stromal cells can recruit immunosuppressive regulatory T (Treg) cells to infiltrate in tumor islands, and overexpression of CCL-17 and its ligand CCR-4 can promote the aggregation of CD4-positive (CD4+) Treg, Th2 and Th17 cells (21, 22).