Although lung cancer mortality has improved in recent years, it remains the leading cancer killer worldwide. Low dose computed tomography (CT) scan screening in high-risk patients has shown improved cancer-specific survival, however, it carries >95% of false-positive rate, a subsequent risk of unnecessary invasive diagnostic biopsy, and repeated radiation exposure. Liquid biopsy assays have been developed to overcome these challenges and to enhance the diagnostic accuracy of CT-screened lung nodules. Among many biomarkers, tumor-derived exosomes (TEXs) have emerged as potent cancer biomarkers. We have discovered a new exosomal marker, Thomsen-Friedenreich glycoantigen (TF-Ag-α; Galβ1-3GalNAc alpha), as a potential biomarker for lung cancer early detection. TF-Ag-α is a unique target expressed on the cell surface of about 84% lung cancers (both nonsmall cell and small cell lung cancer) and other carcinomas (such as breast cancer, colon cancer, etc), but not on normal tissues. Currently there are no reports about TEX TF-Ag-α and its roles in the screening and early detection of lung cancer and other cancers. In this project, we select lung cancer as the disease model and aim to demonstrate the clinical utility of TEX TF-Ag-α in cancer liquid biopsy. To transform our discovery to clinical applications, we have developed a monoclonal antibody, JAA-F11, with high specificity to TF-Ag-α and a surface plasmon resonance (SPR)-based liquid biopsy assay to measure the levels of exosomal TF-Ag-α in blood. We have demonstrated, for the first time, that exosomes carry TF-Ag-α. More importantly, we successfully detected exosomal TF-Ag-α in as low as 10uL serum samples from both early stage and late stage nonsmall cell lung cancer (NSCLC) and small cell lung cancer (SCLC) patients, but little signals from those of normal controls. Based on our promising pilot data, we hypothesize that exosomal TF-Ag-α is a potent biomarker for lung cancer screening and early detection. In this project, we propose to (1) further develop the liquid biopsy assay and comprehensively characterize its sensing performances including analytical sensitivity (limit of detection, limit of quantitation), specificity, linear range, and repeatability; (2) demonstrate the diagnostic values of exosomal TF-Ag-α in lung cancer screening and early detection using both cell-derived exosomes and serum samples from well-defined cohorts of patients including lung cancer patients (both NSCLC and SCLC), individuals with benign pulmonary nodules at high risk of lung cancer and normal controls with no pulmonary nodules (total n=200). We aim to develop an effective cancer specific biomarker and an accurate liquid biopsy assay to complement the diagnosis of pulmonary nodules detected during low dose CT screening and to enhance the accuracy of low dose CT.