ABSTRACT: Background: Blood-based comprehensive genomic profiling (CGP), a form of liquid biopsy, is often used for biliary tract cancer (BTC) when tissue-based CGP (tissue CGP) is unavailable, despite lower detection rates. This study explored factors linked to detecting actionable genomic alterations to optimize its use. Methods: We retrospectively analyzed BTC cases in Japan's C-CAT (June 2019-January 2025), restricting panel comparisons to FoundationOne® CDx (F1; n = 5019) and FoundationOne® Liquid CDx (F1L; n = 1550). Missing covariates were handled by multiple imputations (m = 20). Between-panel balance used 1:1 propensity-score matching (caliper 0.2). Outcomes were modeled with logistic regression. Targets included MSI-H, TMB-H, FGFR2/RET/NTRK fusions, BRAF V600E, KRAS G12C, IDH1 mutations, and ERBB2 amplification. An exploratory analysis stratified results by the number of prespecified enrichment factors (0-4). Liquid biopsy was performed using plasma-based comprehensive genomic profiling assays (FoundationOne® Liquid). Results: Missingness was low; after matching (n = 1549 per group) covariates were well balanced (all|SMD|≤0.05). Detection of any actionable alteration was lower with F1L than F1 (16.8% vs. 24.8%; OR 0.61, 95% CI 0.49-0.75; p < 0.001). F1L also had lower TMB-H (OR 0.62, 0.43-0.90; p = 0.01) and ERBB2 amplification (OR 0.42, 0.31-0.57; p < 0.001), with no significant differences for MSI-H, IDH1, KRAS G12C, or BRAF V600E. Within F1L, non-perihilar location (OR 2.05), liver (1.90), lymph-node (1.41), and lung metastases (1.52) predicted detection of actionable genomic alterations. F1L detection increased from 5.8% (zero factors) to 32.8% (four factors), approximating tissue at three factors. Conclusions: The utility of liquid biopsy can be maximized by carefully selecting samples on the basis of conditions that increase the detection rate.
