Mechanistically, expression of lymphoid homing receptors including CCR4, CCR6, and also CD62L on Treg cells during cancer development leads to the gradually increased number of tumor-associated Treg cells (38) through secretion of CCL17 and CCL22 (ligands for CCR4) by tumor cells as chemotactic factors in early stages of gastric cancer (39). Here, CCR4 is linked to gastric cancer.