Abstract
490 Background: It has been suggested that detection of circulating tumor DNA may be relevant in patients with metastatic colorectal cancer (mCRC). The main objective of the present study was to evaluate a method based on the TaqMan Mutation Detection Assay (TMDA) for the detection of circulating KRAS mutations in mCRC patients. Moreover, we also investigated the prognostic impact of the plasma cell-free DNA and the fraction of circulating KRAS mutations. Methods: The study was conducted from April to July 2013 and plasma samples were prospectively collected in a series of 35 mCRC patients treated with chemotherapy (CT). QIAamp Circulating Nucleic Acid kit was used for DNA extraction and Quant-iT High Sensitivity dsDNA Assay for cf-DNA quantification. Detection of circulating tumor DNA was based on the KRAS mutations detected in tumour and was performed in plasma by the castPCR Technology TMDA. Response to CT was assessed according to RECIST criteria. The results of plasma cf-DNA and level of mutant DNA fragments were correlated with response and 3-months survival. Results: We isolated and quantified plasma cf-DNA in all patients with a mean concentration of 106 ng/mL. Among them, 18 were wild-type and 17 mutated for KRAS in the tumour. Detection of circulating KRAS mutations was performed with TMDA in 23 patients (10 KRAS wild-type and 13 KRAS mutated). The sensitivity was 62% (8/13) and specificity 100% (0/10) with a level of circulating mutant DNA fragments ranging from 0 to 29%. Plasma cf-DNA and level of circulating mutant DNA were both significantly correlated with the 3-months survival (mean 36 versus 524 ng/mL, p=0.0015 and 2% versus 29%, p<0.0001). There was a non significant trend for response to CT (respectively p=0.14 and p=0.12). Conclusions: TMDA method is a simple, accurate and non-invasive tool for the detection of circulating tumor DNA. Our preliminary results also suggest that plasma cf-DNA and fraction of mutant DNA fragments could be prognostic markers in mCRC patients.
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