Background: The aim of this study was to investigate the potential of cell-free DNA (cfDNA) as a disease biomarker\nin oesophageal squamous cell carcinoma (ESCC) that can be used for treatment response evaluation and early\ndetection of tumour recurrence.\nMethods: Matched tumour tissue, pre- and post-surgery plasma and WBCs obtained from 17 ESCC patients were\nsequenced using a panel of 483 cancer-related genes.\nResults: Somatic mutations were detected in 14 of 17 tumour tissues. Putative harmful mutations were observed in\ngenes involved in well-known cancer-related pathways, including PI3K-Akt/mTOR signalling, Proteoglycans in\ncancer, FoxO signalling, Jak-STAT signalling, Chemokine signalling and Focal adhesion. Forty-six somatic mutations\nwere found in pre-surgery cfDNA in 8 of 12 patients, with mutant allele frequencies (MAF) ranging from 0.24 to\n4.91%. Three of the 8 patients with detectable circulating tumour DNA (ctDNA) had stage IIA disease, whereas the\nothers had stage IIB-IIIB disease. Post-surgery cfDNA somatic mutations were detected in only 2 of 14 patients, with\nmutant allele frequencies of 0.28 and 0.36%. All other somatic mutations were undetectable in post-surgery cfDNA,\neven in samples collected within 3-4 h after surgery.\nConclusion: Our study shows that somatic mutations can be detected in pre-surgery cfDNA in stage IIA to IIIB\npatients, and at a lower frequency in post-surgery cfDNA. This indicates that cfDNA could potentially be used to\nmonitor disease load, even in low disease-stage patients.
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