Updated project metadata. Cholangiocarcinomas (CCAs) are heterogeneous biliary cancers with dismal prognosis. Their etiologies remain mostly unclear, although primary sclerosing cholangitis (PSC) is a well-known risk factor. There is an urgent need of accurate non-invasive biomarkers for early CCA diagnosis and to predict patient´s prognosis, which may improve their clinical management and outcome. Here, by high-throughput proteomic analysis of serum extracellular vesicles (EVs), we identified diagnostic and/or prognostic biomarkers specific for CCAs in patients with PSC, and others common to all CCA subtypes. Bulk RNA tissue transcriptomic data revealed that these biomarkers are predominantly expressed in hepatobiliary tissues, being expressed in different liver cell types. Furthermore, single-cell RNAseq (scRNA-seq) analysis revealed that the expression of these biomarkers was preferentially found in malignant cholangiocytes within CCA tumors. In summary, these results highlight the potential of serum EVs to reflect cancer presence, especially for difficult-to-diagnose malignancies, including CCA."