Abstract 493: Quantity of KRAS mutations in cell-free DNA is associated with survival of patients with advanced cancers

Abstract

Abstract Background: Cell-free (cf) DNA from plasma offers an easily obtainable material for KRAS mutation analysis for diagnostics and monitoring. There is emerging evidence that the percentage of mutant cfDNA in the wild-type background (mutant allele fraction, MAF) and/or absolute quantity of mutant cfDNA can be associated with survival of patients with advanced cancers. Methods: Plasma-derived cfDNA from patients with progressing advanced cancers was purified and 16 ng of DNA was tested with a KRAS multiplex assay to distinguish the wild-type allele from 7 of the most common mutations in the G12 and G13 hotspot of exon 2 using the QX200 Droplet Digital PCR™ platform (Bio-Rad). Results were compared to mutation analysis of archival primary or metastatic tumor tissue obtained at different points of clinical care from a CLIA-certified laboratory and clinical outcomes including survival. Results: Of the 117 patients (colorectal cancer, 71; non-small cell lung cancer, 12; melanoma, 10; pancreatic cancer, 5; ovarian cancer, 5; appendiceal cancer, 5; other cancers, 9), KRAS mutations were detected in 85 (73%) archival FFPE tumor samples and 85 (73%) plasma cfDNA samples. The two methods had overall agreement in 109 patients (93%; kappa, 0.83, standard error, 0.06; 95% confidence interval [CI], 0.71-0.94), sensitivity of 95% (95% CI, 0.88-0.99), specificity of 88% (95% CI, 0.71-0.96), even though median time from tissue to blood sampling was 18.5 months (1.1-134.4 months). A higher MAF (>7%) of KRAS in cfDNA as determined by 5% trimmed mean value was associated with shorter survival compared to lower (<7%) MAF (5.4 vs. 7.6 months; P = 0.001), which was confirmed on multivariate analysis. A total of 20 patients with KRAS mutations in cfDNA had longitudinal testing of cfDNA from at least two time points obtained before and on experimental therapy. In these patients, changes in MAF demonstrated a trend towards positive correlation with changes in measurement of target tumor lesions on imaging per RECIST (r = 0.42, P = 0.07). Conclusions: A higher percentage of KRAS mutation in plasma cfDNA is an independent predictive factor for shorter survival in patients with advanced cancers. Citation Format: Kiran Madwani, Helen J. Huang, Dawne N. Shelton, Siqing Fu, Apostolia M. Tsimberidou, Sarina A. Piha-Paul, Aung Naing, David S. Hong, Daniel D. Karp, Debra L. Andrews, Goran Cabrilo, E. Scott Kopetz, Rajyalakshmi Luthra, Bryan K. Kee, Cathy Eng, Van K. Morris, George A. Karlin-Neumann, Funda Meric-Bernstam, Filip Janku. Quantity of KRAS mutations in cell-free DNA is associated with survival of patients with advanced cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 493.