M2 macrophages are characterized by high expressions of PD-L1 and CTLA4 [78], which could not only recruit Treg cells via C-C chemokine receptor 4 (CCR4) to exacerbate the immunosuppressive condition in the cancer microenvironment [79], but also secrete anti-apoptotic cytokines such as TGF-β and epidermal growth factor (EGF) to promote tumor cell proliferation [78]. This evidence concerns the gene CCR4 and cancer.