LAUSR

4520Background: Despite remarkable results with salvage standard-dose (SDCT) or high-dose chemotherapy (HDCT), about 15% of pts with relapsed GCT are incurable. Immune therapy with Pembrolizumab is a novel approach for salvage in pts with metastatic GCT. Methods: Single arm phase 2 trial investigating pembrolizumab 200mg IV Q3weeks until disease progression in pts with relapsed GCT and no curable options. Pts age≥18 with metastatic GCT who progressed after first line cisplatin-based chemotherapy and after at least 1 salvage regimen (HDCT or SDCT) were eligible. Centrally assessed PD-L1 on tumor infiltrating immune cells using PD-L1 (22C3) assay was scored as 0, 1, 2, 3 along with PD-L1 expression score (H-score) incorporating intensity of staining. Pts were eligible irrespective of PD-L1 expression status. The primary endpoint was overall response rate using immune-related response criteria. Simon’s 2-stage design required response in ≥ 1/12 pts to proceed to stage 2 enrolling 8 more pts for a total of 20...