Abstract B036: Pathway repression in progression on osimertinib therapy in NSCLC via a comprehensive genomic and epigenomic circulating tumor DNA (ctDNA) assay

Abstract Background: Osimertinib is currently the most common precision therapy for patients with non- small cell lung cancer (NSCLC) with EGFR mutations. While it prolongs progression-free survival, resistance eventually develops in many, leading to disease progression. Somatic NGS has identified resistance mutations in the EGFR pathway and other oncogenes, but these account for only 40-45% of cases, suggesting non-genetic factors, such as epigenetic changes, may be involved. This study investigates the epigenetic landscape at diagnosis and progression on first- line osimertinib, focusing on cases with and without canonical resistance mutations. Methods: We defined two cohorts from GuardantINFORM, a clinico-genomics database, restricting to only patients with a test on the Guardant Infinity platform, a comprehensive blood-based NGS assay, that analyzes DNA sequence variants and performs extensive methylation profiling (∼15Mb) in >20,000 differentially methylated regions (DMRs) assessed for sample-specific methylation patterns. (A) Diagnosis Cohort: Comprised of 34 NSCLC patients with blood samples collected within six days prior to the initiation of first-line osimertinib therapy. (B) Progression Cohort: Comprised of 36 patients who were on first-line osimertinib therapy, with blood samples collected within 60 days of discontinuation. The progression cohort was further stratified based on the presence or absence of known resistance mutations identified through somatic variant analysis by Guardant360. Gene set enrichment analysis was conducted on these methylation profiles using the Reactome database to define pathway-level differences between the cohorts. Results: Pathway enrichment analysis in the diagnosis and progression cohorts found expected biological processes in NSCLC such as extracellular matrix organization, G- protein coupled receptor (GPCR) signaling, and FGFR pathways. Additionally, the progression cohort lacking canonical resistance mutations (n=23) exhibited unique enrichment in two specific pathways: Glucose-dependent Insulinotropic Polypeptide and Physiological Factors. These pathways include genes such as GATA4, which has been implicated in the epithelial- mesenchymal transition (EMT)—a process associated with transforming to a small cell phenotype, a known mechanism of resistance to EGFR inhibition, including osimertinib. Conclusion: This study demonstrates the utility of epigenetic profiling via liquid biopsies in uncovering non-genetic mechanisms underlying osimertinib resistance in advanced NSCLC. Identification of unique epigenetic pathways in progressing patients without canonical resistance mutations highlights the potential for discovering novel biomarkers of resistance. Further investigation into these findings may advance our understanding of resistance mechanisms across various cancer therapies, particularly for patients without identified genomic resistance, and inform clinical decision-making and trial design. Citation Format: Aaron Hardin, Leslie Bucheit, Amar Das, Craig Eagel, Helmy Eltoukhy. Pathway repression in progression on osimertinib therapy in NSCLC via a comprehensive genomic and epigenomic circulating tumor DNA (ctDNA) assay [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr B036.