KRAS mutations in ctDNA: a promising new biomarker in advanced pancreatic cancer
Authors: C. Montagut, J. Vidal, L. Visa
Journal: Annals of Oncology (2018)

Pancreatic cancer (PC) is predicted to be the second leading cause of cancer-related mortality in the next decade in Western countries [1.Rahib L. Smith B.D. Aizenberg R. et al.Projecting cancer incidence and deaths to 2030: the unexpected burden of thyroid, liver and pancreas cancer in United States.Cancer Res. 2014; 74: 2913-2921Crossref PubMed Scopus (4226) Google Scholar]. Despite recent improvement with the approval of new treatment regimens, such as FOLFIRINOX and gembitabine plus nab-paclitaxel, the prognosis of PC remains dismal with 5-year survival rates of ∼5% [2.Conroy T. Desseigne F. Ychou M. et al.FOLFIRINOX versus gemcitabine for metastatic pancreatic cancer.N Engl J Med. 2011; 364: 1817-1825Crossref PubMed Scopus (5137) Google Scholar, 3.Von Hoff D.D. Ervin T. Arena F.P. et al.Increased survival in pancreatic cancer with nab-paclitaxel plus gemcitabine.N Engl J Med. 2013; 369: 1691-1703Crossref PubMed Scopus (4141) Google Scholar]. The difficulty in obtaining tissue in PC limits the analysis of prognostic and predictive biomarkers to guide treatment decisions. The use of blood biomarkers could be a potential valid alternative. To date, the only serum biomarker approved in international guidelines to monitor response in PC is CA19-9, despite several limitations such as low sensitivity and specificity (∼79% and 82%, respectively) and poor accuracy in the identification of small tumors [4.Ballehaninna U.K. Chamberlain RS. The clinical utility of serum CA 19-9 in the diagnosis, prognosis and management of pancreatic adenocarcinoma: an evidence based appraisal.J Gastrointest Oncol. 2012; 3: 105-119PubMed Google Scholar]. In this context, a minimally invasive effective blood biomarker would be very valuable to predict survival outcome, optimize treatment and monitor therapeutic response in PC patients. PC is characterized by tumor-specific genetic and epigenetic changes in DNA, including frequent mutations in four driver genes, CDKN2A, KRAS, SMAD4 and TP53 [5.Jones S. Zhang X. Parsons D.W. et al.Core signaling pathways in human pancreatic cancers revealed by global genomic analyses.Science. 2008; 321: 1801-1806Crossref PubMed Scopus (3100) Google Scholar, 6.Waddell N. Pajic M. Patch A.M. et al.Whole genomes redefine the mutational landscape of pancreatic cancer.Nature. 2015; 518: 495-501Crossref PubMed Scopus (1687) Google Scholar], which can be detected in ctDNA and potentially be used as prognostic and predictive biomarkers in both early and advanced disease. In the current issue, Kruger et al. explore the role of serial mutKRAS ctDNA measurements as a marker of prognosis, early prediction of response and therapy monitoring in advanced PC patients treated with gemcitabine-based first-line chemotherapy [7.Kruger S. Heinemann V. Ross C. et al.Repeated mutKRAS ctDNA measurements represent a novel and promising tool for early response prediction and therapy monitoring in advanced pancreatic cancer.Ann Oncol. 2018; Abstract Full Text Full Text PDF Scopus (82) Google Scholar]. Furthermore, levels and kinetics of mutKRAS ctDNA are compared with current standard-of-care markers such as CA19-9 and CEA. Whereas Kruger et al. use digital PCR (dPCR) technology—BEAMing—to detect KRAS mutations, previous studies have explored the use of next-generation sequencing (NGS) in PC [8.Sausen M. Phallen J. Adleff V. et al.Clinical implications of genomic alterations in the tumor and circulation of pancreatic cancer patients.Nat Commun. 2015; 6: 7686Crossref PubMed Scopus (307) Google Scholar, 9.Pietrasz D. Pecuchet N. Garlan F. et al.Plasma circulating tumor DNA in pancreatic cancer patients is a prognostic marker.Clin Cancer Res. 2017; 23: 116-123Crossref PubMed Scopus (157) Google Scholar, 10.Cheng H. Liu C. Jiang J. et al.Analysis of ctDNA to predict prognosis and monitor treatment responses in metastatic pancreatic cancer patients.Int J Cancer. 2017; 140: 2344-2350Crossref PubMed Scopus (97) Google Scholar]. From a technical standpoint, NGS and dPCR technologies offer different advantages and disadvantages that make each approach suitable for specific clinical applications. NGS panels offer the advantage to simultaneously detect multiple molecular alterations, but at a higher cost and decreased sensitivity. Among other clinical applications, NGS could be a key tool for simultaneous screening of multiple actionable targets in tumor types with several approved targeted therapies (i.e. lung cancer) or the monitoring of the emergence of multiple co-existing mechanism of resistance (i.e. during anti-EGFR therapy in colon cancer) [11.Montagut C. Argilés G. Ciardiello F. et al.Efficacy of Sym004 in patients with metastatic colorectal cancer with acquired resistance to anti-EGFR therapy and molecularly selected by circulating tumor DNA analyses: a phase 2 randomized clinical trial.JAMA Oncol. 2018; 4: e175245Crossref PubMed Scopus (66) Google Scholar], as well as for discovery. On the contrary, dPCR offers higher sensitivity of mutant allele detection, reaching a detection threshold of 0.001 of mutKRAS alleles per nanograms per milliliters, which makes it a suitable technique for detection of minimal residual disease or screening of specific actionable mutation. Interestingly, because KRAS mutations are very frequent and are a truncal event in PC [5.Jones S. Zhang X. Parsons D.W. et al.Core signaling pathways in human pancreatic cancers revealed by global genomic analyses.Science. 2008; 321: 1801-1806Crossref PubMed Scopus (3100) Google Scholar, 6.Waddell N. Pajic M. Patch A.M. et al.Whole genomes redefine the mutational landscape of pancreatic cancer.Nature. 2015; 518: 495-501Crossref PubMed Scopus (1687) Google Scholar], Kruger et al. use ctDNA KRAS detection and quantification by dPCR as a surrogate marker of tumor load to predict response and treatment monitoring. The authors first assess the concordance between detection of mutKRAS in tissue and plasma, and obtain a perfect specificity (100%) and good sensitivity (75%). The rate of discordant cases with positive KRAS tissue tumor and negative KRAS ctDNA detection are potentially due to low ctDNA shedding explained by low tumor load (when only metastatic patients are considered, the detection rate increases to 79%) and intrinsic pancreatic tumor biology (i.e. stromagenic tumor environment). This high concordance between plasma and tissue is the first necessary step to be able to use mutKRAS ctDNA as a tool for evaluation of response and therapy monitoring. Interestingly, the authors find that the detection of mutKRAS in ctDNA but not in tumor tissue samples is a poor prognosis factor. These data suggest that KRAS is not prognostic by itself but that instead, the release of ctDNA in the bloodstream implies a worse survival, maybe as an indicator of metastatic disease, higher tumor activity or higher tumor burden. The central finding of this study is the value of mutKRAS ctDNA to detect early response in the metastatic setting. The authors find a correlation between mutKRAS ctDNA dynamics and changes in tumor size following gemcitabine-based therapy, as assessed by RECIST criteria. One strength of the study is the homogeneity of the population (consecutive patients with advanced disease treated with gemcitabine-based chemotherapy). Another strength is the high number of serial plasma samples extracted for evaluation (total 284 plasma samples from 54 patients), which allows for a very precise picture of KRAS dynamics in ctDNA. This is important to define the best predictive and prognostic pattern for mutKRAS ctDNA to be used in clinical practice, based on two key characteristics of KRAS blood dynamics: timing and change in mutKRAS mutant allele frequency. In patients without disease progression in the first radiological assessment, authors find a pattern of ctDNA kinetics consisting of an early rise in the levels of mutKRAS ctDNA (day 1 and 2 of treatment) followed by a decrease in mutKRAS levels (days 7–14 of treatment). The authors name this pattern mutKRAS ctDNA normalization. In an effort to develop a more useful tool for daily clinical practice, the authors suggest mutKRAS ctDNA determination at day 14 after treatment initiation as the optimal time point to predict tumor response. Similarly, increases in mutKRAS ctDNA at day 14 are correlated with further progressive disease, with a sensitivity of 83% and a specificity of 100%, that is with no false positive cases. Importantly, the authors find that increases in ctDNA are a better predictor of response to chemotherapy compared with CA19.9, with higher sensitivity and specificity (Figure 1). This study is a proof-of-concept and an important step in the development of noninvasive reliable tools to be used for the prognostic and predictive assessment of advanced PC patients in daily clinical practice. Dynamics in KRAS ctDNA mirror response to treatment, and more importantly they do it as early as 2 weeks after initiation of therapy. This information is crucial for patient management, and should guide clinicians to avoid the toxicity, inconvenience and costs of nonuseful therapeutic agents. Although this is the first large study to show the utility of ctDNA dynamics in metastatic PC, similar findings have recently been described in other tumor types. In metastatic colorectal cancer, changes in mutKRAS ctDNA were shown to mirror tumor response [12.Vidal J. Muinelo L. Dalmases A. et al.Plasma ctDNA RAS mutation analysis for the diagnosis and treatment monitoring of metastatic colorectal cancer patients.Ann Oncol. 2017; 28: 1325-1332Abstract Full Text Full Text PDF PubMed Scopus (220) Google Scholar]. Likewise, Tie et al. also described a group of mCRC patients who had a spike in ctDNA 3 days after initiating treatment, which then rapidly declined in patients with tumor response [13.Tie J. Kinde I. Wang Y. et al.Circulating tumor DNA as an early marker of therapeutic response in patients with metastatic colorectal cancer.Ann Oncol. 2015; 8: 1715-1722Abstract Full Text Full Text PDF Scopus (420) Google Scholar]. Due to the proof-of-concept nature in this study, prospective trials and larger cohorts are warranted to support the integration of liquid biopsy for response assessment in advanced PC. Taken together, Kruger et al. provide a promising first step toward the clinical implementation of a new biomarker with valuable predictive and prognostic information in metastatic PC. More than that, this study adds one more piece of evidence on how liquid biopsy offers a global, noninvasive and real-time genomic information that can potentially help improve the diagnosis, therapeutic strategies and outcome of early and late stage PC patients. CM was supported by ISCiii (CIBERONC CB16/12/00481, PIE15/00008, PI15/00457), Generalitat de Catalunya (2014 SGR 740, Intensificació PERIS) and Fundació Cellex.