CCL17 and neoplasm: CCR4 and its ligands, the thymus and activation regulated chemokine (TARC/CCL17) and the macrophage-derived chemokine (MDC/CCL22), play a key role in development and progression of solid tumors through orchestrating the recruitment and trafficking of immune cells, including the immunosuppressive FoxP3+ CD25+ CD4+ regulatory T cells (Treg) into the lymphoid infiltrates surrounding the tumor [5]–[7].