e23057 Background: Cell-free circulating tumor DNA (ctDNA) has emerged as an effective blood-based biomarker for clinical diagnostics in cancers, improving the accuracy and efficiency of cancer treatment for clinic. However, the somatic mutations originated from inheritance or normal biological metabolism in circulating cell-free DNA (cfDNA) in plasma can largely interfere with the detection of ctDNA. The baseline for ctDNA evaluation is urgently needed for accuracy identification of ctDNAs in patients. Methods: Averagely 20 ml blood samples were collected from more than 1200 individuals including healthy volunteers, lung cancer, colorectal cancer, pancreatic cancer, gastric cancer patients, etc. Genomic DNA from white blood cells and cfDNA from plasma were extracted and constructed as sequencing libraries using a panel contains 50 cancer-associated genes, respectively for each sample. Then they are subjected to ultra-deep sequencing with average depth > 40000 folds covering ~21K nucleotide regions. Results: The background somatic mutation frequencies were detected in genomic DNA and cfDNA in healthy controls. The results showed that most of mutations in cfDNA were consistent with those in genomic DNA. Using data from 1200 individuals, we generated the baseline mutation profiling of cfDNA, which was referred in the ctDNA determination in cancer samples, which significantly improved the accuracy of ctDNA detection compared with tissue biopsy. Conclusions: Our studies demonstrated the importance of sequencing both cfDNA and genomic DNA for ctDNA detection in cancers. We also determined the baseline mutation profiling of circulating cfDNA from more than 1200 healthy individuals and confirmed the value of it by comparing with DNA sequencing data in cancer tissue. Our work offers clue on how to improve the detection accuracy of circulating tumor DNA in early cancer diagnosis.
Circulating cell-free DNA from plasma undergoes less fragmentation during bisulfite treatment than genomic DNA due to low molecular weight