Real-world analysis of ctDNA and other biomarkers in patients with curatively resected stage I-III biliary tract cancer.

4130Background: Growing evidence supports the prognostic and predictive value of circulating tumor DNA (ctDNA) detection in gastrointestinal cancers. Building on previous work that demonstrated the feasibility of tumor-informed ctDNA testing in biliary tract cancer (BTC), this study aimed to evaluate ctDNA as a tool for detecting molecular residual disease (MRD) following curative resection and monitor recurrence during surveillance. Methods: A retrospective analysis of real-world data was performed on patients (N=171) with stage I-III resectable BTC who underwent ctDNA analysis using a personalized, tumor-informed 16-plex mPCR-NGS assay (Signatera; Natera, Inc.) from July 2020-February 2024. Plasma samples (n=769) were collected pre-operatively, postsurgically (within 2 to 12-weeks; MRD window), and longitudinally until death or last follow-up (surveillance window). The prognostic value of ctDNA was compared to traditional biomarkers such as CA19-9 and CEA. Results: A total of 171 patients with stage I-III BTC with a median age of 68 years (range 27-92) were included in this analysis. The median follow-up was 21 months (range: 2-97 months). ctDNA detection rates during the MRD and surveillance windows were 2218/83) and 3235/109), respectively. On evaluating clinical outcomes, ctDNA-positivity during MRD and surveillance was significantly associated with inferior disease-free survival (DFS) and overall survival (OS). Multivariate analysis confirmed ctDNA-positivity to be the most significant prognostic factor associated with DFS (HR: 10.91, 95 3.85-30.9, Plt;0.001) when adjusted for other clinicopathologic factors such as BTC subtype or tumor grade. Additionally, other biomarkers such as CA 19-9 and CEA did not predict clinical outcomes at either the MRD or surveillance windows (Table). Conclusions: The data show that ctDNA-positivity was associated with poor DFS and OS, both in the post-op and surveillance settings and that ctDNA detection using a personalized, mPCR-NGS assay was superior to current clinical biomarkers. These findings highlight the value of ctDNA monitoring to improve prognostication in BTC. Association of biomarkers with clinical outcomes.BiomarkerMRDSurveillancectDNADFS OSn= 83HR: 13.0, p lt; 0.001HR: 12.0, p lt; 0.001n= 109HR: 6.1, p lt; 0.001HR: 17.8, p = 0.008CA19-9DFSOSn= 53HR: 0.88, p =0.81HR: 1.9, p = 0.389n= 80HR: 1.3, p = 0.51HR: 10.1, p = 0.045CEADFSOSn= 18HR: 0.84, p = 0.85HR: 1.7, p = 0.71n= 18HR: 0.54, p = 0.5HR: Not evaluable