Abstract C29: Development of a circulating tumor DNA assay in pancreas cancer

Abstract

Abstract Pancreas cancer is the third most common cause of cancer-related death, owing in part to high rates of unresectable disease at time of diagnosis and poor long-term response to chemotherapy. Biomarkers are needed to sensitively identify and monitor disease burden, and to measure response to therapy. The CA19-9 tumor marker lacks sufficient positive or negative predictive value to guide treatment decisions, and digital droplet PCR (ddPCR) assessment of circulating KRAS mutations suffers poor sensitivity on account of only assessing a single DNA locus. We hypothesize that a multitargeted circulating tumor DNA assay can outperform CA19-9 and ddPCR as biomarker for the detection and monitoring of pancreas cancer. Our lab has developed the cancer personalized profiling by deep sequencing (CAPP-Seq) method, which combines high-depth sequencing with several strategies of error-suppression to identify minute amounts of tumor DNA circulating in patients’ blood. The development of our CAPP-Seq targeted sequencing panel hinged primarily on capturing regions of the genome known to be recurrently mutated in pancreatic ductal adenocarcinoma (PDAC), based on The Cancer Genome Atlas project. These regions contain mutations in KRAS, TP53, SMAD4, and by a long-tail of mutations in many other genes for which we contributed approximately 200 kb of selector space. In addition to recurrent SNVs, we also contributed approximately 35 kb for recurrent copy number variant locations, 10 kb for recurrent noncoding variants, and 20 kb for regions with aberrant expression patterns in PDAC based on TCGA RNA-sequencing data. This purpose of this study is to employ CAPP-Seq in two pancreas cancer cohorts: patients who underwent resection at Stanford and had blood drawn before and after surgical resection (n=30), and a cohort of patients with metastatic disease who are undergoing chemotherapy with blood draws at multiple time-points (n=20). The former cohort will assess prediction of recurrence based on ctDNA level, and the latter will assess patients with early development of resistance to chemotherapy. Before assessing this ctDNA detection assay in patients with pancreas cancer, we first evaluated the CAPP-Seq approach on two healthy research subjects and achieved on average 4000x de-duplicated sequencing depth, for a theoretical limit of detection of 0.03% circulating tumor fraction. We next sequenced samples from 7 patients with resectable disease and 8 with metastatic disease, with results expected in early July. Citation Format: Dan King, Mari Olsen, George Fisher, Max Diehn, Ash Alizadeh. Development of a circulating tumor DNA assay in pancreas cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr C29.