Targeted deep sequencing of circulating tumor DNA in metastatic pancreatic cancer

// Andreas W. Berger 1 , Daniel Schwerdel 1 , Thomas J. Ettrich 1 , Alexander Hann 1 , Stefan A. Schmidt 2 , Alexander Kleger 1 , Ralf Marienfeld 3, * and Thomas Seufferlein 1, * 1 Department of Internal Medicine I, Ulm University, 89081 Ulm, Germany 2 Department of Diagnostic and Interventional Radiology, Ulm University, 89081 Ulm, Germany 3 Institute of Pathology, Ulm University, 89070 Ulm, Germany * These authors contributed equally to this work Correspondence to: Thomas Seufferlein, email: Thomas.seufferlein@uniklinik-ulm.de Keywords: circulating tumor DNA; liquid biopsy; pancreatic cancer; tumor evolution; tumor heterogeneity Received: April 25, 2017 Accepted: December 08, 2017 Published: December 16, 2017 ABSTRACT Purpose: Precision medicine in pancreatic ductal adenocarcinoma (PDAC) could be substantially supported by tools that allow to establish and monitor the molecular setup of the tumor. In particular, noninvasive approaches are desirable, but not validated. Characterization of circulating tumor DNA (ctDNA) may help to achieve this goal. Experimental Design: Blood samples from patients with metastatic PDAC prior to and during palliative treatment were collected. ctDNA and corresponding tumor tissue were analyzed by targeted next generation sequencing and droplet digital PCR for the 7 most frequently mutated genes in PDAC (TP53, SMAD4, CDKN2A, KRAS, APC, ATM, and FBXW7). Findings were correlated with clinical and imaging data. Results: A total of 20 patients (therapy naïve n = 11; pretreated n = 9) were included. All therapy naïve patients ( n = 11/11) presented with detectable ctDNA at baseline. In pretreated patients, 3/7 (prior to 2nd line treatment) and 2/2 (prior to 3rd line chemotherapy) had detectable ctDNA. The combined mutational allele frequency (CMAF) of KRAS and TP53 was chosen to reflect the amount of ctDNA. The median CMAF level significantly decreased during treatment ( P = 0.0027) and increased at progression ( P = 0.0104). CA19-9 analyses did not show significant differences. In treatment naïve patients, the CMAF levels during therapy significantly correlated with progression-free survival (Spearman, r = −0.8609, P = 0.0013). Conclusions: Monitoring of ctDNA and its changes during treatment may enable to adapt therapeutic strategies to the specific molecular changes present at a certain time during treatment of mPDAC.