Abstract: Background Lung cancer in never-smokers represents 10-25% of lung cancers worldwide; ranks among the most common causes of cancer mortality; and has a distinct natural history, predominant histological subtype (adenocarcinoma), different profile of oncogenic mutations, and response to targeted therapy compared to lung cancer in smokers. There are few known environmental and genetic risk factors for lung cancer in never-smokers; however, a large fraction of cases cannot be explained. One promising approach to identify etiological factors involved in lung tumorigenesis in never-smokers is the study of “mutational signatures” that exogeneous and endogenous processes leave on the tumor and surrounding tissue. This approach has identified 50+ mutational signatures in other cancer types, corresponding to several oncogenic processes. Method We are conducting an integrative genomic analysis of mutational signatures in tumors and surrounding non-tumor lung tissue from 2,000 never-smokers. Study subjects include a subset of “special exposure cases” exposed to high levels of known risk factors (n=∼500) and “general population cases” without known risk factors (n=∼1,500). Subjects are drawn from studies with lung tissue samples and high-quality epidemiological and clinical data. We are striving to include subjects from many geographical areas and ethnic groups to study the contribution of different germline and environmental factors. The tumor/normal genomics analysis are ongoing and include whole genome sequencing (WGS), RNA sequencing, and genome-wide methylation arrays. The integrated molecular landscape will be ordered along the evolutionary trajectory of the tumors to infer the cascade of events leading to tumor formation and progression. Data on the molecular and evolutionary landscape will be combined with data from histological examination of H&E slides from multiple tissue blocks per tumor and related to CT imaging to provide a more refined classification of lung cancers among never-smokers. Additional studies will include lineage phylogenetic analysis to infer the clonal evolution of lung tumors using multi-region tumor sampling; deep target sequencing of cancer driver genes and ultra-low pass WGS of cell-free circulating tumor DNA; tumor microenvironment analyses based on immunohistochemistry or fluorescence-based imaging and RNA sequencing; and analyses of large-scale electronic medical records. Result: Preliminary results will be shown, highlighting the large differences in the molecular landscape of lung cancer in never-smokers from that of smokers. Conclusion This comprehensive study will improve our understanding of the etiology and progression of lung cancer in never-smokers and provide clues into prognosis and treatment.