Extrachromosomal DNA in lung cancer from never smokers

Abstract Extrachromosomal DNA (ecDNA), circular DNA that resides outside of the linear chromosome, is a potent form of oncogene amplification in cancer. The structure and properties of ecDNA are markedly different from those of linear DNA, characterized by features like non-Mendelian inheritance and an altered epigenetic landscape. A prior pan-cancer analysis ​​indicated patients with cancers harboring ecDNA have statistically worse overall survival when compared to cancer patients with other types of focal amplification. Moreover, its unique characteristics also make it a promising target for therapy. Recently, efforts have intensified to profile ecDNA across many cancer types, yet comprehensive studies of ecDNA in lung cancer in never smokers (LCINS) is lacking. Given that LCINS is partially driven by somatic copy number alterations, we hypothesized that ecDNA-driven focal amplifications significantly influence LCINS tumor evolution. As part of the Sherlock-Lung project (current data freeze, 1217 samples), we comprehensively profiled 871 treatment-naive samples using a robust computational pipeline that refined copy number segmentation by accounting for tumor purity and ploidy. ecDNA was present in 151 (17.3%) of tumor samples, with a third of ecDNA-positive samples harboring more than one distinct ecDNA amplicon. Consistent with prior reports, no ecDNA was found in bulk sequenced blood or matched normal lung tissues. These ecDNA often included genes (84%), frequently overlapping with known oncogenes like MDM2, TERT, and MYC, which showed higher expression levels compared to non-amplified or other amplified genes. Notably, most MDM2 amplifications (36/45) were on ecDNA. ecDNA was significantly associated with whole genome doubling, tumor stage, and several endogenous mutational signatures, including APOBEC (SBS2 and SBS13), and clock-like signature (SBS1). Intriguingly, ecDNA-positive tumors were associated with significantly worse survival compared to tumors without any focal amplifications, though tumors with other amplification types (e.g. breakage-fusion-bridge, linear amplification, or complex events) had similar survival impacts. The unprecedented size of our cohort and the integration of clinical, epidemiologic, and multi-omics data allowed us to perform the first in-depth characterization of ecDNA in LCINS. We reconstructed the genomic regions involved in ecDNA and revealed the full spectrum of simple and complex ecDNAs across cancer histologies as well as the clinical and functional impact of ecDNA on LCINS. Citation Format: Azhar Khandekar, Tongwu Zhang, Marcos Diaz-Gay, Jens Luebeck, Ludmil Alexandrov, Maria Landi. Extrachromosomal DNA in lung cancer from never smokers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB286.