The objective of the study is to reveal the acquired resistance mechanism of the first and second generation Epidermal Growth Factor Receptor-Tyrosine Kinase Inhibitor (EGFR-TKI) in tissue and plasma using Next Generation Sequencing (NGS) and the difference of ctDNA in plasma and DNA in biopsy samples is compared and the consistency of two samples was observed. At the same time, the sensitivity, specificity and the consistency of detecting T790M mutation using ddPCR, Cobas and NGS were compared.

With the deepening of the concept of tumor management, it is necessary to monitor the patient's gene during the course of treatment, especially in patients with acquired resistance of the first generation EGFR-TKI. Re-biopsy can effectively provide tissue samples as a "gold standard" for gene detection samples. While, the plasma circulating tumor DNA (ctDNA) detection is an important sample of gene detection and the treatment when tissue samples cannot be assessed. However, due to tumor heterogeneity and ctDNA detection technique sensitivity, plasma ctDNA and tissue samples of the test results are inconsistent. Therefore, the difference between re-biopsy tissue samples and plasma ctDNA samples will provide strong evidence for the application of plasma ctDNA in TKI-resistant patients.

The study was designed as a prospective and single center study. Fifty patients will be enrolled into the study and the clinical data of patients, including smoke history, cancer history, location, pathology, gene mutation status and so on of the first biopsy samples will be collected and recorded in a case report form. For patients recruited in the study, lesions which were assessed as progressive disease(PD) will be obtained by interventional pulmonology technology. And about 20ml peripheral blood will be collected at the same time. The tissue will be divided into two parts, one part was sent to Pathology Department of Shanghai Chest Hospital and will be processed with paraffin-embedded, and for those diagnosed NSCLC, the other part will be extracted with DNA and performed NGS for the qualified DNA sample and using Cobas to detect the T790M mutation. The matched peripheral blood will also be extracted with DNA and performed NGS and ddPCR.

Inclusion Criteria:

1. EGFR mutations were confirmed by molecular pathology.
2. Patients who were treated by the first and the second generation EGFR-TKI.
3. Patients were evaluated PD according to RECIST imaging standard.
4. Patients with functional status score (Performance Status, PS) for 0-2 points according to the Eastern Cooperative Oncology Group (ECOG) .
5. Patients can receive histological / cytological specimens through microsurgical biopsy techniques, including but not limited to transbronchial biopsy (TBB), transbronchial lung biopsy (TBLB), transabonchial needle aspiration (TBNA), CT / ultrasound guided thoracic needle aspiration biopsy (CT / ultrasound guided-TTNA), ultrasound-guided superficial lymph node biopsy.

Exclusion Criteria:

1. Patients received blood transfusion within 1 month.
2. Patients suffering from autoimmune diseases, including but not limited to systemic lupus erythematosus, class of wet arthritis, Sjogren's syndrome.
3. Patients with severe disease is not suitable for medical biopsy.
4. Patients refused to participate in clinical trials.
5. Researchers consider that the patient is not suitable for participating in this clinical trial.