Prospective evaluation of circulating tumor DNA sequencing in pancreatobiliary carcinomas.

107 Background: Pancreatobiliary carcinomas (PC) carry a poor prognosis but have not yet benefitted from the revolution in precision oncology, in part because biopsy tissue is often inadequate for molecular characterization. Cell-free DNA (cfDNA) sequencing tests may provide access to genetic testing and monitoring for advanced PC patients. Methods: Twenty-five advanced PC patients were enrolled prospectively in a trial to assess the feasibility, accuracy, and clinical utility of cfDNA next-generation sequencing (NGS) of 54 cancer genes. cfDNA mutations were compared to those detected by biopsy-based NGS tests, and the concordance of the two was determined. cfDNA sequencing in disease monitoring was compared to changes in secreted tumor markers in a subset of patients. Results: The NGS-based cfDNA test detected cancer mutations in 21 of 25 (84%) advanced PC patients and provided actionable findings for four patients. Multi-gene sequencing data was available from both blood-based and biopsy-based methods f...