Abstract 5240: Comparative levels of KRAS mutations circulating tumor DNA for association with overall survival in patients with non-resectable pancreatic cancer
Authors: Johansen Julia S. , Vibat Cecile Rose T. , Hancock Saege , Hassaine Latifa , Samuelsz Errin , Chen Inna , Collisson Eric A. , Calatayud Dan , Jensen Benny V. , Hasselby Jane Preuss , Lu Timothy T. , Poole Jason C. , Melnikova Vlada , Erlander Mark G. 
Published: August 2015

Background: The median overall survival (OS) time of patients with non-resectable pancreatic cancer varies widely. Diagnostic tools are presently lacking to predict patient outcome at diagnosis. The vast majority of pancreatic tumors harbor KRAS mutations. In this study, we evaluated whether quantitative baseline and longitudinal monitoring of KRAS mutations in plasma circulating tumor DNA (ctDNA) may be used to stratify patients for predicting outcome.

Methods: The Danish BIOPAC study prospectively collected plasma from patients with non-resectable pancreatic cancer undergoing treatment with gemcitabine or FOLFIRINOX. Archival (3-5 years) plasma specimens were collected from 113 patients pre-treatment (baseline),on chemotherapy, as well as at multiple additional time intervals for up to 977 days from baseline. Interim analysis of ctDNA KRAS was conducted (after 105 deaths). Levels of ctDNA KRAS mutations were assessed in 35 patients with long OS (median 473 days; range 360-1134), 33 patients with medium OS (median 227 days; range 155-349) and 37 patients with short OS (median 94 days; range 21-146). PCR enrichment of KRAS G12A/C/D/R/S/V, and G13D mutations was performed, followed by massively parallel deep sequencing and quantification with standardization of reporting number of copies detected per 105 genome equivalents (GE).

Results: In a prospective-retrospective biomarker study of 113 patients, interim analysis of ctDNA KRAS was conducted (after 105 deaths). 92 of 105 patients had evaluable baseline plasma samples. Number of mutant KRAS copies was higher in patients with short OS (median 661; range 0-190,490 copies/105 GE) versus with median OS (median 103; range 0 to 275,918 copies/105 GE) versus with long OS (median, 15; range, 0-1,369 copies/105 GE). Longitudinally, KRAS mutation levels remained mostly low with long OS (last time point median 9; range 0-70,451 copies/105 GE) vs. medium OS (median 155; range 0-314,103 copies/105 GE) or short OS where levels increased or remained high (median 803; range 0-138,508 copies/105 GE). As this dramatic difference in systemic KRAS levels may reflect distinct tumor phenotypes, the underlying tumor biology was further investigated by interrogating additional cancer mutational hotspots (using massively parallel deep sequencing) in plasma ctDNA of patients stratified by systemic KRAS and the OS.

Conclusion: Shorter OS in patients with non-resectable pancreatic cancer tended to associate with high levels of ctDNA KRAS mutations at diagnosis and with post-treatment elevation of KRAS mutations. ctDNA KRAS mutation levels in patients with non-resectable pancreatic cancer observed at diagnosis or on treatment may predict patient outcome and could reflect distinct underlying tumor biology.

Citation Format: Julia S. Johansen, Cecile Rose T. Vibat, Saege Hancock, Latifa Hassaine, Errin Samuelsz, Inna Chen, Eric A. Collisson, Dan Calatayud, Benny V. Jensen, Jane Preuss Hasselby, Timothy T. Lu, Jason C. Poole, Vlada Melnikova, Mark G. Erlander. Comparative levels of KRAS mutations circulating tumor DNA for association with overall survival in patients with non-resectable pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5240. doi:10.1158/1538-7445.AM2015-5240