CD4 and cancer: Lymphocytes are key cells in the tumor microenvironment, and according to their profile have different functions in cancer progression: CD8+ T cells lyse tumor cells and release cytokines enhancing cytotoxic responses, such as IFNγ; CD4+ Th1 T cells release cytokines improving lymphocyte cytotoxic function; regulatory CD4+ T cells (Treg) are immunosuppressive cells, preventing chronic inflammation and maintaining immune tolerance, by suppressing effector T cell proliferation and activation (17, 20).