RESEARCH ARTICLE Circulating Free DNA as Biomarker and Source for Mutation Detection in Metastatic Colorectal Cancer

Background Circulating cell-free DNA (cfDNA) in plasma has shown potential as biomarker in various cancers and could become an importance source for tumour mutation detection. The objec-tives of our study were to establish a normal range of cfDNA in a cohort of healthy individu-als and to compare this with four cohorts of metastatic colorectal cancer (mCRC) patients. We also investigated the prognostic value of cfDNA and analysed the tumour-specific KRASmutations in the plasma. Methods The study was a prospective biomarker evaluation in four consecutive Phase II trials, includ-ing 229 patients with chemotherapy refractory mCRC and 100 healthy individuals. Plasma was obtained from an EDTA blood-sample, and the total number of DNA alleles and KRAS mutated alleles were assessed using an in-house ARMS-qPCR as previously described. Results Median cfDNA levels were higher in mCRC compared to controls (p<0.0001). ROC analy-sis revealed an AUC of 0.9486 (p<0.00001). Data showed impaired OS with increasing lev-els of baseline cfDNA both when categorising patients by quartiles of cfDNA and into low or high cfDNA groups based on the upper normal range of the control group (Median OS 10.2 (8.3–11.7) and 5.2 (4.6–5.9) months, respectively, HR 1.78, p = 0.0006). Multivariate analy-sis confirmed an independent prognostic value of cfDNA (HR 1.5 (95 % CI 1.3–1.7) for each increase in the cfDNA quartile). The overall concordance of KRASmutations in plasma and tissue was high (85%)