ctDNA in Genetic Profiling and Clinical Outcomes of Advanced Biliary Tract Cancer

Biliary tract cancer (BTC) is a heterogeneous and aggressive malignancy with poor prognosis, especially in advanced or metastatic stages where surgical resection is not feasible. The current standard first-line therapy with gemcitabine and cisplatin provides limited survival benefit, with median overall survival around 11-12 months. Targeted therapies, such as FGFR inhibitors for FGFR2 fusions and IDH1 inhibitors, as well as immune checkpoint inhibitors, have improved outcomes in subsets of patients. However, tumor tissue acquisition remains challenging in BTC, limiting the ability to perform comprehensive genomic profiling. Circulating tumor DNA (ctDNA) has emerged as a promising biomarker for molecular profiling, treatment monitoring, and prognosis assessment. Prior studies demonstrated acceptable concordance between ctDNA-based and tissue-based next-generation sequencing, particularly for FGFR2 fusions, and highlighted the potential of ctDNA in identifying additional genomic alterations not detected in tissue samples. This prospective study will enroll 100 Korean patients with advanced or metastatic BTC from 11 hospitals. Approximately two-thirds of patients will provide blood samples prior to first-line systemic therapy, while one-third will provide samples before subsequent therapy. Additional blood draws will be performed at progression in patients harboring FGFR2 fusion, IDH1 mutation, or HER2 amplification. Collected samples will be analyzed by a central laboratory (SCL Healthcare, a precision medicine service provider specializing in biomarker-based diagnostics). The primary objective is to evaluate the frequency of actionable genomic alterations, especially FGFR2 fusions, detected by ctDNA in advanced BTC patients. Secondary objectives include: * Assessing the concordance between ctDNA and tissue genomic profiling * Evaluating the proportion of patients who received targeted therapy based on ctDNA results (e.g., pemigatinib \[Pemazyre®\]) * Exploring associations between ctDNA maximum variant allele frequency (max VAF) and survival outcomes * Identifying potential resistance mechanisms and clonal evolution during targeted therapy This study is expected to provide robust evidence for the clinical utility of ctDNA in BTC and contribute to the establishment of precision medicine approaches, potentially supporting future guideline development and regulatory approval of ctDNA assays in Korea and globally.