Cell-free DNA as biomarker and source for mutation detection in primary colorectal cancer

Purpose: To analyze if cell free (cf)DNA levels and the presence of KRAS and BRAF mutations in serum could be used as diagnostic biomarkers in patients with primary colorectal cancer (CRC). Methods: This study included 92 individuals who were operated due to primary CRC (N=52;study group) and to hemorrhoids (N=40;control group). Serum cfDNA levels were measured with real-time PCR (RT-PCR) using PicoGreen dsDNA quantitation reagent. Colorectal tissue and related blood and serum samples taken at the time of surgery were subjected to DNA extraction and analysis of KRAS and BRAF mutations based on multiplex SNaPshot assay and DNA sequencing. Results: The average cfDNA concentration was lower in patients of the study group (20 +/- 7 ng/mu L) in comparison to controls (34 +/- 9 ng/mu L) and this difference was statistically significant (p<0.001). The SNaPshot analysis detected KRAS c35 mutations in colorectal tumor tissue in 14 cases, but the presence of the mutation was not confirmed in cfD-NA extracted from blood samples of these patients. Conclusions: The level of serum cfDNA in CRC is decreased in comparison to patients with hemorrhoids, which questions the usefulness of cfDNA as cancer biomarker. Also, cfDNA does not appear to be suitable as a source for mutation detection in this disease.