Quantitative monitoring and mutations of ctDNA before and after non-small cell lung cancer radical surgery

Objective The aim of this study was to study the quantitative expression of circulating tumour DNA(ctDNA) in patients with non-small cell lung cancer(NSCLC) before and after radical operation and to explore the correlation between gene mutations in non-small cell lung cancer tissues and those in ctDNA.Methods We randomly assigned 5 NSCLC patients from the Department of Thoracic Surgery of Fujian Medical University Union Hospital. All the patients had undergone radical surgery. Venous blood samples were collected from the 5 NSCLC patients at two time points(before the operation and 21–37 days after the operation) for monitoring ctDNA levels. This was done by isolating plasma from venous blood using high velocity centrifugation, extracting DNA from the plasma using the QIAamp Circulating Nucleic Acid kit, and then quantifying the ctDNA levels. The results were analyzed using the Wilcoxon Rank Sum Test. Moreover, the ctDNA levels were compared with those of carcinoembryonic antigen(CEA), which was detected simultaneously with the ctDNA. Then, DNA samples from the tumor tissues and peripheral blood cells and ctDNA were sequenced using the Hiseq2000 sequencing platform(Illumina) and the mutant genes were screened out. Mutations that occurred within the tumor tissues were used as positive control, whereas those found in the pre-operative blood cells were used as a negative control. Based on the mutational analysis of ctDNA genes, a total of 508 cancer-related genes were screened. Results The median values of the pre-and post-operative ctDNA levels in the 5 patients with NSCLC were 0.612(0.518–0.876) and 0.430(0.372–0.612) ng/μL, respectively. There was a significant difference between the two groups(P < 0.05). The pre-operative CEA level was slightly higher than the post-operative level(P > 0.05). In one of the cases, LC tissues showed multiple mutations, consistent with pre-operative ctDNA. Moreover, isogenic mutations of the same type were not detected in post-operative ctDNA or peripheral blood cells. Conclusion Mutations found in the lung cancer(LC) ctDNA gene were consistent with the mutation type of LC tissue. Hence, the quantitative and qualitative analysis of ctDNA is a promising novel molecular biomarker for the evaluation of tumor burden changes in NSCLC.