Abstract 3251: Insights from liquid biopsy testing in clinical settings: Analysis of an Indian dataset

Abstract While solid tumor profiling by tissue Next Generation Sequencing(NGS) is now undertaken routinely in the clinical setting, the availability and adoption of cell free (cf) DNA based NGS assays is limited in the Indian context. This retrospective study assesses the utility of liquid biopsy testing using a validated targeted panel in a clinical setting.A total of 495 plasma samples were analyzed for single-nucleotide variants, indels, copy-number variants, and gene fusions using a targeted unique molecular identifier (UMI) based 74-gene liquid biopsy panel. The panel covers all genes with a Tier 1 drug recommendation for therapy,and additional Tier 2 genes for prognosis or added clinical impact. Variants were assessed for clinical significance,and classified using AMP guidelines. Actionability was defined as the presence of Tier 1 or Tier 2 alterations with therapeutic, prognostic or diagnostic relevance.The most common tumor types tested were NSCLC (43.2%), colorectal cancer (12.1%), and breast cancer (10.1%), followed by hepatobiliary, prostate, pancreatic, and ovarian cancers. Overall, 61.4% of samples (304/495) harbored at least one actionable alteration, with Tier 1 variants detected in 26.5% of the cases. The mean number of alterations in actionable cases was 2.0. The overall actionability of 61.4% was comparable to the actionability obtained from a similar cohort of tissue samples analyzed on the solid biopsy version of this panel (68.3% of 621 cases), thus highlighting the sensitivity and high clinical yield of this panel. The actionability for each cancer type was high for certain cancers; NSCLC (62.1%; n=214), colon (56.7%; n=60), breast (70.0%; n=50) , hepatobiliary (57.6%, n=33, and carcinoma of unknown primary (46.4%, n=28). The most frequently mutated gene overall was TP53, detected in 36.36% of the cases.The distribution of the variant allele frequency (VAF) was also examined. Across 617 reportable events, VAFs ranged from 0.15% to 92.0%. The median VAF was 3.97%, and the 75th percentile was at 19.8%, consistent with the clinical settings in which liquid biopsy is used. 2% of cases had variants with VAF 75%, and these were all found to be in EGFR or TP53, suggestive of copy-number gains in these genes in late-stage disease. Additionally, ESR1 resistance mutations were detected in 11 of the 50 breast cases, underscoring the utility of liquid biopsy in detecting markers of acquired resistance.This analysis thus demonstrates that a compact, guideline-aligned ctDNA panel provides robust detection of clinically meaningful alterations across diverse solid tumors. High rates of actionability, together with the identification of resistance-associated events, support the value of liquid biopsy as a practical and informative tool for precision oncology. Citation Format: Urvashi Bahadur, Aarthi Ravichandran, Bhanumathy G, Sreelaksh Raju, Suhasini Narain, Kaushiki K, Kalainanghi Neelagandan, Anusha N J, Aishwarya Ramkumar, Saman Sajjad, Dhanashree A. More, Ramya Raviprakash, Tanvi Mathur, Srivathsan Adimoolam, Mahalakshmi Prakash, Divya Priya A, Anitha N R, Suruchi Aggarwal, Swetha Nayanala, Shanmukh Katragadda, Sameer Phalke, Vamsi Veeramachaneni. Insights from liquid biopsy testing in clinical settings: Analysis of an Indian dataset abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3251.