CTLA4 and prostate carcinoma: While this observation could suggest PD-L1 is a more dominant checkpoint pathway that is activated during ENZR CRPC, it is important to highlight that responses to Ipilimumab in prostate cancer patients does not always correlate with high frequency of CTLA-4+T cells [26] and it is unknown whether expression of CTLA-4 ligands CD80/86 on antigen presenting cells correlate with positive or negative responses to CTLA-4 blockade.