Real World Study of Icotinib in Adjuvant Post Surgical Treatment for Stage IA2 High Risk to IB EGFR Mutant Non Small Cell Lung Cancer

Inclusion Criteria: * 1\. Histologically confirmed primary non small cell lung cancer (NSCLC), predominantly non squamous histology (including adenocarcinoma or mixed carcinoma with a major adenocarcinoma component) * 2\. Pathologically confirmed stage IA2 high risk to IB NSCLC following complete surgical resection (R0) of primary lung cancer. Disease staging follows the 8th edition of the AJCC/UICC lung cancer staging system. * 3\. Post surgical tumour tissue specimens test positive for EGFR sensitizing mutations using an approved assay * 4\. Patients in the control group received postoperative observation without any anti tumour therapy prior to disease recurrence or metastasis. Exclusion Criteria: * 1\. A history of other malignancies within 5 years prior to lung cancer surgery, with the exception of curatively treated malignancies. * 2.Prior receipt of systemic anti-tumor therapy for NSCLC within 6 months before lung cancer surgery or before disease recurrence and metastasis.