Programmed death-ligand 1 (PD-L1) expression in cured and not cured testicular and other germ cell tumors (GCT).

485 Background: PD-L1 is involved in immune regulation and is prognostic in many tumor types. The aim of this study was to assess PD-L1 expression in orchiectomy and metastases (mets) from GCT and to assess for an association with outcome. Methods: Immunohistochemistry (IHC) on whole sections from archival formalin-fixed paraffin-embedded tissue from Dana-Farber Cancer Institute (DFCI) and Gustave Roussy (IGR) was performed using anti-PD-L1 antibody E1L3N. Stained slides were scored semi-quantitatively and assessed independently. At DFCI, PD-L1 was scored as percent of positive tumor cells (TC) and extent of positive immune cell (IC) infiltrate; at IGR, a cut-off of 5% defined positive TC and IC. PD-L1 status was assessed by site, histology and chemotherapy (CT) status. PD-L1 status was correlated with clinical outcome. Most samples at DFCI were pre-CT (74.2%) whereas most at IGR were post-CT (85.4%). Results: IHC from 171 patients with GCT (89 DFCI, 82 IGR) from 1987-2014 was reviewed. The DFCI cohort in...