Abstract 2490: Quantification of tumor fraction and outcomes association in a real-world non-small cell lung cancer (NSCLC) cohort using a tissue agnostic epigenomic circulating tumor DNA (ctDNA) assay

Abstract Background: The validity of ctDNA assays for evaluating molecular response to therapy by measuring changes in variant allele fraction (VAF) while on treatment is well established, but they are prone to limitations such as low ctDNA levels and interference from copy number variation and clonal hematopoeisis (CH), which may be overcome by methylation-based quantification. ctDNA levels may be monitored throughout a patient's (pts) journey to indicate when relapse or progression is present, often sooner than current methods (RECIST). Here we describe the performance of a methylation-based ctDNA assay to quantify ctDNA levels and correlate changes with outcomes in a real-world NSCLC cohort. Methods: RADIOHEAD is a pan-tumor observational study of 1200 patients on standard of care ICI treatment regimens with plasma samples collected prospectively for retrospective analysis. We randomly selected 241 NSCLC pts that have a combined total of 761 samples (236 baseline, 191 C3D1, and 128 at 6 months post first dose). Samples were analyzed using a commercial NGS assay, which quantifies circulating tumor fraction (cTF) via interrogating thousands of methylation sites from ctDNA, validated with LoB, LoD, LoQ, and linearity studies. Cox proportional hazards (CPH) were used for comparison of real-world progression free survival (rwPFS). Gender, age, disease stage, and blood-assessed tumor mutational burden (bTMB) were included as covariates. Median rwPFS was calculated using Kaplan Meier analysis. rwPFS ordinal groups were defined as PFS event within 3mo, 3-6mo, 6-12mo, and greater than 12mo, and association with early ctDNA changes was assessed with a chi-squared test. Results: In this cohort, 4, 11, 83 and 142 pts were stage I to IV, respectively (1 unknown). Methylation based detection of ctDNA at baseline or C3D1 was associated with shorter rwPFS (baseline: mPFS 12. 7 mo 9. 3-19. 5 vs NR 16. 4-NR; HR=2. 2 1. 3-3. 7 p0. 005, C3D1: mPFS 12. 4 mo 9. 3-16. 1 vs NR 19. 5-NR HR= 2. 2 1. 3-3. 5, p0. 005) independent of stage, gender, or age. Longer rwPFS was associated with 95% reduction in cTF from baseline to C3D1 or low ctDNA at both timepoints (rwPFS 3mo = 12. 5%, 3-6 mo = 30. 8%, 6-12 = 37. 1%, ≥12 mo = 55. 3%; N=153, p=0. 015). For pts with ctDNA not detected at C3D1, ctDNA detection at 6 months post first dose was strongly associated with shorter rwPFS (mPFS 13. 5 mo 9. 5-NR vs. NR 19. 5-NR; HR= 6. 2 1. 9-20. 1, p0. 005). Conclusions: These data demonstrate a significant association of ctDNA detection via methylation-based cTF and on-treatment changes in cTF with rwPFS. Furthermore, subsequent cTF detection 6-months on-treatment, without cTF detected early on-treatment was associated with worse outcomes, suggesting the value of serial monitoring to improve identification of patients likely to progress. Citation Format: Sara Wienke, Sean Gordon, Samantha Liang, Jing Wang, Reagan Barnett, Kyle Chang, Shile Zhang, Carin R. Espenschied, Katie Quinn, Kimberly Banks. Quantification of tumor fraction and outcomes association in a real-world non-small cell lung cancer (NSCLC) cohort using a tissue agnostic epigenomic circulating tumor DNA (ctDNA) assay 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 (6Suppl): Abstract nr 2490.