Pan-cancer landscape of CD274 (PD-L1) and PDCD1LG2 (PD-L2) structural variations.

3133 Background: PD-1 receptor and PD-L1 ligand interactions are the target of immunotherapies across multiple tumor types. Established biomarkers that predict response to immunotherapy are microsatellite instability, tumor mutational burden, and PD-L1 immunohistochemistry. Structural variations in CD274 (PD-L1) and PDCD1LG2 (PD-L2) have been observed in cancer, but the comprehensive landscape is unknown. Here we describe the genomic landscape of CD274 and PDCD1LG2 structural variations, their potential impact on the tumor microenvironment, and evidence that patients with these alterations can benefit from immunotherapy. Methods: We analyzed sequencing data from 514 cancer cases with CD274 and PDCD1LG2 structural variations across 25 publications and data sources, including large pan-cancer sources: Foundation Medicine, Inc (FMI), The Cancer Genome Atlas (TCGA), and Oncology Research Information Exchange Network. To evaluate immune signature enrichment, we ran the software ImSig on gene expression data. We curated literature reporting clinical outcomes of patients harboring structural variations in CD274 and PDCD1LG2. Results: From 25 studies and datasets, we curated 514 cancer cases with structural variations in PD-L1 and PD-L2, including 158 duplications, 126 deletions, 97 inversions, 178 translocations, and 96 unclassified structural variations, totaling to 655 events. We observed breakpoint ‘hotspots’ in the 3’-untranslated regions (UTRs) of PD-L1 and PD-L2. Leveraging TCGA data, we observed, in CD274-rearranged tumors, significant upregulation in PD-L1 and PD-L2 expression and signatures for interferon signaling, macrophages, monocytes, T cells, and immune cell proliferation (each p < 0.001, compared to CD274 non-rearranged, copy neutral tumors). Furthermore, retrospective review of 12 studies that included patients with structural variations in CD274 or PDCD1LG2, including duplications, inversions and copy number amplifications, revealed a 73% (52/71) response rate to PD-1 immunotherapy with durable responses. Conclusions: Our evaluation of CD274 and PDCD1LG2 structural variations shows that the 3’-UTR is frequently affected and is associated with increased expression of ligands and immune signatures. Enriched interferon signaling in CD274-rearranged tumors is of particular interest, as interferon exposure is known to drive PD-L1 and PD-L2 expression. Retrospective evidence from curated studies suggests that these genomic alterations could identify candidates for PD-1 or PD-L1 immunotherapy. We expect that these findings will better define CD274 and PDCD1LG2 structural variations in cancer and support our pan-cancer prospective clinical trial to target these alterations.