Correlation of PDL1 tumor expression and outcomes in renal cell carcinoma (RCC) patients (pts) treated with pazopanib (paz).

3021 Background: The interaction between PDL1 (B7H1) and its receptor PD-1 on activated T cells plays an important role in the inhibition of T-cell responses and contributes to suppression of antitumor immune responses. Tumor PDL1 expression has been associated with poor outcomes in RCC. This study investigates the correlation between PDL1 tumor expression and outcomes in RCC pts treated with paz. Methods: Using IHC, we retrospectively analyzed baseline FFPE tumor samples for PDL1 from 2 paz RCC studies: a single arm phase II trial and randomized placebo (pbo)-controlled phase III study. PDL1 expression was analyzed by MedTox Laboratories using the anti-PDL1 MouseIgG1 clone 5H1 (Thompson) on the Leica automated IHC platform. Additional dual PDL1/CD68 staining was carried out to delineate tumor and macrophage PDL1 expression. Tumor PDL1 expression was quantified by H-Score (HS) and PDL1+ macrophages were assessed semi-quantitatively. Association between PDL1H scores and PFS was investigated by Kaplan-Meier...