EGFR-TKI是当前EGFR敏感突变晚期肺癌患者有效的治疗手段。然而，除少部分原发耐药之外，其余治疗有效的患者也不可避免地继发耐药。高敏感的基因检测手段发现，所谓的耐药突变在TKI治疗前就以低拷贝量存在，认为TKI对耐药型突变的"克隆选择"作用可能导致了继发耐药，但具体机制并不清楚。新近发现，肿瘤微环境中基质细胞分泌的HGF可激活MET信号通路，致使BRAF基因突变的黑色素瘤对RAF抑制剂产生耐药。我们认为异质性（狭义上肿瘤细胞之间及广义上肿瘤细胞和基质细胞之间的异质性）是导致敏感突变肺癌产生EGFR-TKI原发性和继发性耐药的根本原因，且具有阈值和量效关系。本研究拟采用Transwell共培养和RNAi等技术，通过细胞系和移植瘤动物实验，深入研究EGFR野生型、T790M耐药突变型肺癌细胞，以及基质细胞对EGFR敏感突变型肺癌细胞发生TKI耐药的影响和作用机制，并探索解除耐药的方法。

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) is an effective targeted drug in the treatment of advanced non-small cell lung cancer with EGFR-activating mutations. A small part of patients result in primary resistance to EGFR-TKI, however, almost all of the rest patients responding to EGFR-TKI treatment will inevitably acquire secondary drug resistance. Using highly sensitive detection method, researchers found so-called resistant genetic variations such as EGFR T790M mutation and MET gene amplification, could exist as a low-copy number in tumors before EGFR-TKI treatment, suggesting that "clonal selection" for TKI-resistant mutations subjected to EGFR-TKI treatment leads to secondary resistance to EGFR-TKI. However, the exact mechanism is not yet clear. Recently, a study published in journal "Nature" in 2012 indicated that microenvironment stromal cells surrounding the cancer cells could secrete hepatic growth factor (HGF) and activated its receptor MET, which made patients suffering from melanoma with BRAF mutation result in resistance to RAF inhibitor. According to the current studies, we hypothesized that heterogeneity is the most important mechanism for primary and secondary resistance to EGFR-TKI in NSCLC patients with EGFR activating mutations, which might has a threshold and dose-effect correlation. Heterogeneity includes the heterogeneity between tumor cells with various EGFR statuses, as well as heterogeneity between tumor cells and stromal cells in tumor microenvironment. The purpose of this project is to study the influences of lung cancer cells with wild-type or T790M mutation EGFR, as well as stromal cells on sensitivity of lung cancer cells with EGFR-activating mutations to EGFR-TKI using Transwell co-culture and RNAi etc. technologies in vitro cells lines and in vivo xenograft models, and further explore the way to restore the sensitivity of cancer cells.