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

Abstract

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 included 69 orchiectomy, 15 mets and 5 unknown origin with 28 total deaths; the IGR cohort included 26 lung mets, 36 mediastinal or retroperitoneal lymph node mets and 20 primary mediastinal tumors. DFCI had 38 seminoma (S), 50 nonseminoma (NS) and 1 unknown; at IGR, 13 S and 69 NS. In both cohorts, PD-L1 staining in IC was higher in S (DFCI 33/38 moderate (mod)-high (86.8%); IGR 12/13 positive (92.3%)) vs. NS (DFCI 26/50 mod-high (52.0%); IGR 35/68 positive (51.5%)) (DFCI p = 0.003; IGR p = 0.006). At DFCI, 5 samples had PD-L1 positive TC (2 mixed GCT, 2 pure choriocarcinomas (CC) and 1 S); at IGR, 14 had positive TC (all NS, including 11 pure CC). More PD-L1 positive TC were CC than other GCT types (DFCI p = 0.003; IGR p < 0.001). In 36 S orchiectomy samples at DFCI, 0/4 that scored none-mild died and 2/31 (6.5%) that scored mod-high died (p = 1.00); in 30 NS orchiectomy samples, 4/9 (44.4%) that scored none-mild died and 2/16 (12.5%) that scored mod-high died (p = 0.14). Conclusions: Higher PD-L1 status in orchiectomy is not associated with GCT survival. PD-L1 positive TC may serve as a histological marker for CC among NS. Higher PD-L1 expression on IC in S and on TC in CC may point to immunotherapy as a therapeutic option in these tumors.