(UroToday.com) The KEYNOTE-427 trial was a phase II international trial of the anti-PD-1 monoclonal antibody pembrolizumab as monotherapy in metastatic renal cell carcinoma. This agent showed promising activity as monotherapy in both clear cell and non-clear cell histologies, with some association between PD-L1 positivity as measured by Combined Positivity Score (CPS ≥ 1. The CPS score is measured by the number of PD-L1 staining cells (tumor and microenvironment), divided by the number of viable tumor cells and multiplied by 100. The association between PD-L1 positivity by CPS score and therapeutic outcome in patients treated with non-immunotherapy based regimens is unknown.