Lung cancer is the leading cause of cancer deaths in both men and women in the United States, with over 155,000 patients dying each year in this country alone. Several factors contribute to the poor outcome of lung cancer patients, but, as in most solid tumors, the ability of cancer cells to leave the primary tumor and establish inoperable metastases is a major impediment to successful therapy. Metastasis thus represents a major clinical challenge that is driven by as yet poorly understood cell state alterations. This proposaluses novel methods to uncover the molecular and cellular changes that underlie lung cancer progression and each step of the metastatic cascade. We will use a genetically-engineered lung adenocarcinoma mouse model that recapitulates the genetic alterations and histological progression of human lung adenocarcinoma. In Aim1, we will functionally interrogate lung cancer metastasis-promoting and -inhibiting genes in vivo, by using a lentiviral vector system to directly express rational candidate regulators of lung cancer metastasis in developing tumors in vivo. We will combine these tools with a genetically-engineered mouse model of lung adenocarcinoma which incorporates fluorescent marking of cancer cells to allow quantification of each step of the metastatic cascade. In Aim2, we will isolate lung adenocarcinoma cells from primary tumors and metastases by fluorescence activated cell-sorting to uncover gene expression profiles that define each stage of malignant progression. Gene expression changes that direct metastatic ability will help define potential biomarkers of the malignant disease stateand reveal the relationship of global gene expression in primary tumors and their related metastases in different organs. In Aim3, we will analyze and functionally dissect gene function during human lung adenocarcinoma progression, through the correlation of candidate gene expression in human lung adenocarcinoma with clinical outcome and use of a defined lung epithelial cell transformation system to assess gene function both in cell culture and in vivo. Given the immense clinical impact of metastatic cancer and the current gap in understanding the molecular underpinnings of this disease state, both clinical practice and patient outcome would be greatly impacted by any new therapies that might result from the fundamental knowledge gained from our proposed analyses. By combining quantitative methods and powerful in vivo methods, we hope to uncover general principles that govern tumor progression and metastatic spread and ultimately uncover novel therapeutic targets across the continuum of cancer progression.