Lung cancer is a malignant tumor with high morbidity and mortality worldwide. The incidence and mortality of lung cancer in China have topped the list of malignant tumors since 2010.Early diagnosis and effective intervention are extremely important in the clinical treatment of lung cancer. Surgical resection could achieve better prognosis in patients with early lung cancer (stages IA and IB).For patients with advanced lung cancer (stages II, III, and IV), individualized treatment with molecular classification researches and the application of targeted drugs based on the pathological classification, molecular genetic characteristics, and body conditions of patients has been confirmed to effectively prolong the lifetime. However, the lack of effective and convenient detection approaches for capturing oncology information of patients, promoting early diagnosis and effective intervention of lung cancer, and ultimately improving the prognosis of lung cancer are limitations in achieving successful clinical treatment of lung cancer.

At present, methods used in clinical screening of lung cancer,including detection of serological markers, imaging technology, and biopsy ,have some limitations:in the absence of imaging evidence, the serological assessment could not be used as the evidence for diagnosis and treatment strategy alteration for lung cancer. The application of low-dose computed tomography scan for lung cancer screening shows a high false-positive rate, which is liable to require excessive medical treatment. Biopsy does greater harm to patients with lung cancer; sampling is difficult, and effective information may be missed because of tumor heterogeneity. With the development of molecular pathology in cancer research in recent years, liquid biopsy has become an important developmental direction for clinical tumor detection because of its noninvasiveness, convenient sampling, and potential for overcoming tumor heterogeneity.Liquid biopsies include the detection of circulating tumor cells (CTCs), tumor exosome (exosome), circulating tumor RNA (ctRNA), and circulating tumor DNA (ctDNA) in peripheral blood.

ctDNA is a part of circulating free DNA (cfDNA), which is released by tumor cell necrosis, apoptosis, micrometastasis, or the cleavage of CTCs and proliferated tumor cells.ctDNA includes genetic information of tumor cells, such as mutation, recombination, and deletion (15). ctDNA was approved by the European Medicines Agency in 2014 and the National Comprehensive Cancer Network Guidelines for NSCLC in 2017 as a supplement sample to assess genetic variation when tumor tissue samples were difficult to obtain. Clinical studies have shown that ctDNA can effectively reflect tumor load, malignant degree, metastasis ability, and real-time information of genetic mutation, which has a certain correlation with the genetic information of tumor tissues. Moreover, the content of cfDNA in patients with cancer was significantly higher than that in healthy people. Also, ctDNA has been used for detecting tumor load, monitoring tumor recurrence, and assessing minimal residual disease in a number of cancer types. Some studies have suggested that ctDNA can be used to estimate tumor recurrence, even before imaging. Therefore, ctDNA detection has an important value in the clinical application of lung cancer diagnosis, drug efficacy, surgical effect evaluation, recurrence monitoring, prognosis judgment, medication guidance, and molecular classification differentiation.

This study intends to include 400 patients with stage I-III lung cancer. The capture sequencing of lung cancer-related genes in peripheral blood ctDNA and tumor tissue DNA will be performed during the diagnosis and treatment process using the liquid-phase hybridization approach. Thus, the study will establish a large sample size database of the genetic variants in patients with lung cancer during the diagnosis and treatment process, and promoted the development of an individualized diagnostic model of the lung cancer population. The patients with lung cancer undergoing surgery will be followed up, and the plasma concentration of cfDNA and genetic mutation of ctDNA will be detected to evaluate the postoperative residual cancer, monitor tumor recurrence, and timely guide the clinical treatment and intervention. The molecular classification differentiation analysis and screening of tumor recurrence-related genetic mutations will be performed after the surgery and during the course of disease progression to provide the referential clinical research model and ideas for the application of ctDNA detection-based liquid biopsy technique in tumor therapy.