PD-1 expression on classical monocytes (CM) as an independent predictor of cancer specific survival in clear cell renal carcinoma (ccRCC).

562 Background: We have previously shown that PD-1 expression in peripheral blood lymphocytes is elevated in RCC patients at diagnosis and decreases subsequent to surgery. We theorize that classical monocyte (CM) inhibition through PD-1 interferes with antigen presentation necessary to stimulate adaptive immune responses, and, thus, preop CM PD-1 expression is prognostic of poor outcomes. Methods: Blood samples were obtained from RCC patients (n = 90) preop and age-matched healthy donors (n = 25). Flow cytometric (FC) data were quantified as mean fluorescence intensity (MFI) or % of cells that express a biomarker. Patients were excluded if they had comorbid CLL, had prior surgeries for RCC, had non-ccRCC histology, or if the FC data was missing. We have defined elevated CM PD-1 expression at the third quartile level of CM PD-1 expression (784 MFI) in the healthy donors. CM PD-1 level was correlated with patient clinico-pathologic data using non-parametric tests. Cancer specific survival (CSS) curves were ...