Liquid biopsy and biomarkers in pancreatic ductal adenocarcinoma: from concept to clinical translation—a narrative review

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal malignancies because most patients are diagnosed at an advanced stage when curative treatment is no longer feasible. Conventional tools such as cross-sectional imaging and carbohydrate antigen 19-9 (CA19-9) have limited sensitivity for early detection and for minimal residual disease (MRD) assessment. This narrative review focuses on developments from 2018 to 2026, a period marked by rapid maturation of multi-analyte and multi-omics liquid biopsy platforms. We emphasize integrating circulating biomarkers into a unified “circulome” framework and critically evaluate their performance across clinical contexts, including high-risk surveillance, symptomatic diagnosis, MRD detection, and treatment monitoring.