Treatment monitoring of metastatic colorectal cancer by quantification and genotyping of mutated KRAS in circulating cell-free DNA.

Abstract

e15037 Background: Treatment of stage IV colorectal cancer (mCRC) has made substantial progress over the last years but therapy monitoring still is in its early stage. A facile, non-invasive, repeatable assessment of the mutational state of a given tumor even during treatment could constitute a desirable biomarker for therapy stratification and disease monitoring. "Liquid biopsies" analyzing circulating free and circulating tumor DNA (cfDNA/ctDNA) from patients’ blood have been proposed as a a simple, non-invasive method that could fulfil this requirement. Methods: 27 patients with histologically confirmed mCRC were enrolled into a treatment surveillance cohort. For the analysis of concordance between tumor tissue DNA and cfDNA we analyzed 40 tissue and blood pairs from therapy naïve patients regarding their KRAS mutation status. The course of cfDNA values combined with targeted genotyping of KRAS mutations were assessed during several palliative chemotherapeutic regimens. cfDNA data were correlated with clinical parameters to establish its prognostic and predictive value. Results: Baseline cfDNA levels allow to significantly differentiate mCRC from healthy controls (14.23 ± 6.33 ng/ml vs. 2.60 ± 1.59 ng/ml; p < 0.0001). cfDNA values at baseline in therapy naïve patients correlate well with tumor burden (p < 0.05) and CEA levels (p < 0.05). cfDNA values significantly increased upon disease progression during 1st (p < 0.01) and 2nd line (p < 0.05) treatment, enabling a non-invasive disease monitoring approach. Moreover, there was a significant correlation between the cfDNA levels upon treatment and progression-free survival (p < 0.05). In addition, our data show that KRAS genotyping of cfDNA under therapy is feasible (80% blood-tissue concordance) and might benefit the patient due to early detection of therapy resistance. Conclusions: Repetitive quantitative and mutational analysis of cfDNA is likely to complement current diagnostic standards in stage IV CRC over the whole continuum of treatment.