IntroductionOncogenic EGFR is the most common driver mutations by which targeted therapies in NSCLC through their ability to induce dramatic and durable responses. However, almost all patients will eventually have disease progression resulting from drug resistance. Therefore, understanding the resistance mechanism remains essential to prevent or delay the emergence of resistance by EGFR mutations. TKIs resistance generally were considered to be acquired as for that occurred or more easily to be detected of a secondary mutation in the targeting process that interferes with inhibition.The present study set out to investigate the EGFR mutation status in circulating tumour cells and pathological specimens from patients with untreated lung cancer.Material and methodsPeripheral blood samples (4.5 mL) were collected from 91 patients with lung cancer (lung cancer group), 10 patients with benign lung diseases and 10 healthy volunteers (control group). Circulating tumour cells (CTCs) were then enriched by positive immunomagnetic separation with an anti-CD326 antibody, detected by immunocytochemistry with anti-cytokeratin/anti-EpCAM/anti-CD45 antibody and Hoechst staining, and processed by an MMI CellEctor for single-cell selection. Subsequently, CTC DNA was amplified, and the EGFR gene was analysed by the amplification refractory mutation system (ARMS) and NGS.Results and discussionsThe CTC capture rate in lung cancer patients was 61.5% (56/91), whereas no CTCs were detected in patients with benign lung disease or healthy volunteers. The positive CTC detection rate in patients at TNM stage III and IV was 69.3% (52/75) and 25.0% (4/16), respectively. The number of CTCs captured from patients with small cell lung cancer was significantly higher than that from patients with other pathological types of cancer. In patients positive for EGFR mutations, the detection rate of EGFR mutations in a single CTC was very low (6.25%, 1/16). Other inconsistent EGFR mutations were observed among CTCs derived from the same patient with lung adenocarcinoma. There was notable heterogeneity among EGFR and driver gene mutations in different samples from the same patient.ConclusionA simplified technique for isolating CTCs from blood was established. Based on pure CTC DNA amplification and analysis, our data clearly show significant gene heterogeneity in NSCLC patients before treatment.