Erlotinib Combined With Chemotherapy in TKI Resistant Non-Small Cell Lung Cancers

The investigators will enroll patients diagnosed with advanced non-squamous,non-small cell lung cancer, patients with EGFR TKI sensitive mutations and developed TKI resistance in first line treatment. After enrollment, the investigators will do biopsy again before second line treatment to find out the potential mechanism of TKI resistance, do EGFR mutation test for both sensitive and resistant mutation in exon 18, 19, 20 and 21; do KRAS, BRAF and PI3K mutation test, do FISH for MET and HER-2, the investigators do all these test to evaluated both primary and secondary resistance, the investigators do all these tests to get an overview for EGFR mutation status of each patient who develop TKI resistance. For second line treatment, patients will received a 28 days gemcitabine platinum combined with erlotinib scheme, after 4 cycle of combined chemotherapy, patients will receive erlotinib for further treatment until progression disease. For the patients who have stable brain metastases, combined chemotherapy should begin after local treatment, such as whole brain radiotherapy or sterotactic radiosurgery. the main endpoint of this study is mean PFS, second endpoints of this study consist of mean OS, 8 week ORR.