Abstract 4643: A novel epigenomic profiling assay reveals disease biology and therapeutic targets in gastro-esophageal cancer from 1 ml of plasma

Abstract INTRODUCTION: Gastro-esophageal adenocarcinoma (GEA) is an aggressive and heterogeneous disease with a poor prognosis. Targeted therapies have failed largely due to challenges associated with biopsy collection, tumor antigen heterogeneity, and accurately distinguishing transcriptionally distinct esophageal, GE junction or gastric tumor types. We developed a novel, multimodal liquid biopsy assay that profiles genome-wide transcriptional activation. Here, we deploy this assay to define clinically relevant insights in a cohort of GEA patients. METHODS: 1 ml of plasma from whole blood samples was used to assess genome-wide enhancer, promoter and DNA methylation loci in 11 GEA patients (Stage III: 1, Stage IV: 10) and 7 healthy volunteers. 6 patients were confirmed as HER2+ based on standard tissue IHC/ISH methods. ctDNA estimation was performed using the ichorCNA algorithm on low pass whole genome sequencing data. A multimodal HER2 classifier developed previously using genome-wide features including HER2 was used to predict HER2 status of the GEA samples. RESULTS: Epigenomic profiling and comparison of GEA and healthy volunteer plasma samples revealed distinct genome-wide transcriptional activation patterns associated with gastroesophageal adenocarcinoma, including (i) the characteristic upregulation of HER2, FGFR2 and VEGF (ii) SOX2, KLF4, GATA6 transcription factor circuitry, and (iii) DNA methylation at the CHFR and MGMT promoters. We then explored if epigenomic profiling of liquid biopsies could infer the activation status of antibody-drug conjugate (ADC) targets currently under investigation in GEA cancers. Simultaneous examination of multiple target genes including HER2, HER3, TROP2, CLDN18, CEACAM5 and MET demonstrated patient-specific differences and dynamic range in transcriptional activation of a subset of these target genes. Finally, we investigated if HER2 status could be assigned accurately and quantitatively from a liquid biopsy using the multimodal HER2 classifier. HER2 positivity by IHC was predicted accurately in 8/11 samples corresponding to an area under the ROC curve (AUC) greater than 0.85. Discordance between plasma and tissue HER2 calls could be partially attributed to variability associated with tumor site/section used for tissue collection, IHC staining, and time between biopsy collection and blood draw. CONCLUSIONS: We demonstrate the feasibility of comprehensive epigenomic profiling from low input volume of 1ml of plasma to provide a snapshot of the tumor’s transcriptional state to derive clinically actionable insights. The HER2 classifier overcomes several of the challenges with IHC profiling by providing a uniform and quantitative measurement of HER2 activation. This non-invasive assay provides an accurate reflection of tumor transcriptional biology that can inform optimal patient selection strategies. Citation Format: Jonathan Beagan, Aparna Gorthi, Anthony D'Ippolito, Travis Clark, Michael Coyne, Tyrone Tamakloe, Amy Donahue, Baovy Tran, Hyun-Hwan Jeong, Kristian Cibulskis, Hathairat Sawaengsri, Corrie A. Painter, Juliann Chmielecki, J Carl Barrett, Mosammat Faria Afreen, Aditya Pandey, Ilexa Ashley Schechter, Martin S. Taylor, Matthew R. Strickland, Matthew Eaton, Samuel J. Klempner. A novel epigenomic profiling assay reveals disease biology and therapeutic targets in gastro-esophageal cancer from 1 ml of plasma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4643.