Increased Treg infiltration in the tumour microenvironment through C-C chemokine receptor 4 (CCR4) [109] with the high expression level of the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and PD-1 markers was linked with a poor prognosis in prostate cancer [110,111]. Here, CTLA4 is linked to prostate cancer.