Abstract 3659: Development of customized circulating tumor DNA panel for minimal residual disease detection in biliary tract cancer
Authors: Shinohara Yoshihito , Low Siew-Kee , Nakamura Toru , Kimura Yasutoshi , Murakami Takeshi , Kiyotani Kazuma , Hirano Satoshi 
Published: March 2024

Abstract
Biliary tract cancer (BTC) is a rare type of abdominal cancer and is more frequent in Asian countries than in Western. The 5-year survival rate for BTC is very low 7 to 20% and only 20% of BTC patients could undergo curative-intent surgery. BTC diagnosis based on biopsy and cytology are low in sensitivity that prompted the necessity to identify alternative biopsy. Liquid biopsy, specifically circulating tumor DNA (ctDNA) is known for the accessibility and low invasiveness received great interest for their potential uses in various clinical applications for patients with insufficient tumor tissue, including mutation profiling, treatment monitoring, and cancer detection. However, the panel available in the market up-to-date focused mainly targeted, actionable alterations and thus not suitable for minimal residual disease (MRD) monitoring. In this study, we aimed to develop a customized ctDNA panel for MRD monitoring in BTC. In this study, 124 BTC patients undergone curative resections were enrolled at Hokkaido University and Sapporo Medical University from May 2019 to April 22. All enrolled patients have BTC diagnosis confirmed by pathological diagnosis after surgery, and without other malignant tumors. Genomic profiles of FFPE tissue were conducted using Ampliseq CCP. 13 patients were excluded for high fragmentation. Referring to the genomic profiles of 111 patients in our study and 1924 patients in TCGA established a customized panel using Ion Ampliseq HD technology. The Ampliseq HD panel claims to detect variants at 0.1% LOD for ctDNA detection. It also integrates molecular barcodes to reduce NGS-related errors. The designed panel was 258 Amplicons and 20 genes including eleven therapeutically targetable genes. Clinical characteristics of ctDNA detection were also assessed. Results:The panel validation: concordance of the mutation allele frequency (MAF) between the NGS standard control and Ampliseq HD panel showed a coefficient of determination (R2) of 0.96. Also, concordance of MAF Ampliseq CCP and Ampliseq HD panel on FFPE tumor profiling showed R2 of 0.78. When assessing 70% of BTC patients were covered to have at least one tumor-derived Ampliseq HD panel. When assessing using plasma cell-free DNA, 55% of BTC patients were detected to have at least one tumor-derived ctDNA. Distribution of detected altered top4 genes using Ampliseq HD panels shows TP53 35%, KRAS 10%, SMAD4 5%, ARID1A 2.5%. Clinical characteristics may affected the concordance of plasma and FFPE tumor tissue; stage (P=0.035), size of tumors (P=0.0088), subtype (P=0.013), LN metastasis (P=0.11). Conclusions: A highly sensitive ctDNA customized panel for BTC was established. We also found that clinical characteristics of the BTC affects the detection of ctDNA from blood liquid biopsy. Future study: MRD evaluation using this customized panel.
Citation Format: Yoshihito Shinohara, Siew-Kee Low, Toru Nakamura, Yasutoshi Kimura, Takeshi Murakami, Kazuma Kiyotani, Satoshi Hirano. Development of customized circulating tumor DNA panel for minimal residual disease detection in biliary tract cancer [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 3659.