Abstract 3130: Extrachromosomal DNA in the cancerous transformation of Barrett’s esophagus
Authors: Luebeck Jens , Ng Alvin W. , Galipeau Patricia C. , Li Xiaohong , Katz-Summercorn Annalise , Kim Hoon , Jammula Sriganesh , He Yudou , Verhaak Roel , Maley Carlo C. , Alexandrov Ludmil B. , Fitzgerald Rebecca C. , Paulson Thomas G. , Chang Howard Y. , Wu Sihan , Bafna Vineet , Mischel Paul S. 
Published: April 2023

Abstract
Oncogene amplification on extrachromosomal DNA (ecDNA) drives rapid tumor evolution, treatment resistance, and poor outcomes for patients. Computational tools can detect ecDNA in whole-genome sequencing (WGS) data from biopsies. However, the lack of longitudinal studies tracking patients from pre-cancer to cancer have made it difficult to determine how ecDNAs contribute to the malignant transformation. Two independent surveillance studies of Barrett’s esophagus (BE) patients enabled us to study this transition, as BE is the precursor lesion of esophageal adenocarcinoma (EAC). The studies included a longitudinal case-control study and an independent, cross-sectional surveillance cohort, both with histological correlatives, providing an unprecedented opportunity to study the role of ecDNA in the transition of BE to EAC.
We analyzed WGS data from 206 patients in a cross-sectional surveillance cohort from Cambridge University UK, with biopsy-validated BE, including 42 patients who never developed high-grade dysplasia (HGD) or EAC during multi-year follow-ups, 25 patients with HGD, 51 patients with early-stage EAC, and 88 patients with late-stage EAC. ecDNA frequency increased between early-stage EAC (24%) and late-stage EAC (43%), suggesting continual ecDNA formation during cancer progression.
We additionally analyzed WGS and histology data collected from multi-regional sampling of BE and EAC tissue at two time points from 80 BE patients in an observational case-control study at the Fred Hutchinson Cancer Center (FHCC), where 40 of the patients developed BE-associated EAC during the study and 40 did not. Among FHCC patients, 33% who developed EAC had at least one esophageal biopsy with ecDNA prior to, or at EAC diagnosis. In biopsies collected before cancer diagnosis, ecDNA presence in the biopsy was enriched among patients who later developed EAC compared to patients who did not. When linked to histology data, ecDNA-positive biopsies associated with worsened histological states before cancer diagnosis (p=0.015), and also at cancer diagnosis (p=0.037), with the pre-cancer timepoint being on average 2.1 years prior to cancer diagnosis. The ecDNAs had diverse collections of oncogenes and immunomodulatory genes, and showed higher copy number states than other focal amplification types. Furthermore, ecDNAs showed increasing copy number and structural complexity in more advanced disease stages highlighting their positive selection and ongoing structural evolution. In both FHCC and Cambridge cohorts, we found an association of TP53 loss with ecDNA formation demonstrating the role of prior genomic instability to form ecDNA. In total, our findings illustrate that oncogenic ecDNA can develop early in the malignant transformation, and that they are tied to worsening patient disease status.
Citation Format: Jens Luebeck, Alvin W. Ng, Patricia C. Galipeau, Xiaohong Li, Annalise Katz-Summercorn, Hoon Kim, Sriganesh Jammula, Yudou He, Roel Verhaak, Carlo C. Maley, Ludmil B. Alexandrov, Rebecca C. Fitzgerald, Thomas G. Paulson, Howard Y. Chang, Sihan Wu, Vineet Bafna, Paul S. Mischel. Extrachromosomal DNA in the cancerous transformation of Barrett’s esophagus [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3130.