Abstract A030: Pancreas-specific circulating cell-free DNA for detection of occult metastases and prognosis in resectable pancreatic ductal adenocarcinoma
Authors: Till Jacob E. , Ben-Ami Roni , Shemer Ruth , Kim Kristine , Abdalla Aseel , Cannas Samuele , Vollmer Charles M. , O'Hara Mark H. , Stanger Ben Z. , Dor Yuval , Carpenter Erica L. 
Published: November 2022

Abstract
Up to 85% of patients with resectable pancreatic ductal adenocarcinoma (PDAC) experience metastatic relapse after curative intent surgery with many recurring early. Detection of such occult metastases (those thought to be below the level of detection of standard of care imaging at the time of resection) could steer patients to a different treatment course rather than delaying systemic therapy until after recovery from inappropriate surgery. Here we investigate the potential of pancreas-specific circulating cell-free DNA (cfDNA) as a biomarker for the detection of occult metastatic disease and as a prognostic biomarker. Blood specimens were collected from 53 patients (15 negative control healthy subjects, 11 positive control metastatic PDAC patients, and 27 resectable PDAC patients prior to resection), processed to plasma, and banked. Plasma cfDNA was extracted, quantified, treated with bisulfite, and used as template for PCR amplification of 9 marker loci that are uniquely unmethylated in DNA of pancreatic acinar or duct cells. Following deep sequencing of PCR products, the fraction of cfDNA molecules derived from the pancreas was determined and multiplied by the total cfDNA concentration to yield pancreas-specific cfDNA. Recurrence and survival data were abstracted from the medical record and receiver operator curve analysis was utilized to determine statistical significance. Metastases were categorized as overt (present at diagnosis), occult (discovered during or within 4 months of curative intent surgery), or two-year (discovered during or within two years of curative intent surgery). Pancreas-derived cfDNA was significant for the detection of occult or overt metastases in our full cohort (18 of 52 evaluable subjects) with an area under the curve (AUC) of 0.86 (95% Confidence Interval, 0.74-0.80) and 0.91 (0.83-1.00) for liver-specific occult or overt metastases (15 of 52). It was borderline significant for the detection of occult metastases in the resectable sub-cohort (7 of 27) with an AUC of 0.71 (0.47-0.96) but significant for the detection of occult liver-specific metastases (5 of 27) with an AUC of 0.79 (0.62-0.96). Further, detection of overt metastases or two-year metastases (28 of 50) was significant with an AUC of 0.85 (0.74-0.96). In the resectable sub-cohort, it was also significant for the detection of two-year metastases (17 of 25) with an AUC of 0.79 (0.60-0.97) and prognostic for 2-year overall survival (12 of 24) with an AUC of 0.81 (0.62-1.00) in the resectable sub-cohort. Liver-derived cfDNA was also analyzed and was always outperformed by pancreas-specific cfDNA. In this pilot cohort, enumeration of pancreas-specific cfDNA shows promise as biomarker of occult metastatic disease, two-year metastatic progression, and two-year overall survival in resectable PDAC. Further investigation of a larger cohort and potential combination with other known markers like CA19-9 and tumor size is underway; results for an additional ~40 patients will be available by the time of the meeting.
Citation Format: Jacob E. Till, Roni Ben-Ami, Ruth Shemer, Kristine Kim, Aseel Abdalla, Samuele Cannas, Charles M. Vollmer, Mark H. O'Hara, Ben Z. Stanger, Yuval Dor, Erica L. Carpenter. Pancreas-specific circulating cell-free DNA for detection of occult metastases and prognosis in resectable pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr A030.