In stage 3 NSCLC, treatment and follow-up are generally performed in a 'one-size-fits-all' manner. In the setting of metastatic lung cancer there has been considerable success identifying biomarkers, which allow treatments to be tailored and lead to more personalised medicine. In patients with stage 3 disease there exists a significant unmet clinical need for equivalent biomarkers to guide treatment decisions such as to identify poor responders, predict benefit from treatment and diagnose relapse before standard of care imaging. Recent advances have made it possible to detect and quantify circulating-tumour DNA in peripheral blood of patients with stage 3 NSCLC, a promising prognostic biomarker and a measure of minimal residual disease. In addition, the information contained in routine medical images and electronic patient reported outcome measure (ePROM) questionnaires can add further predictive power to circulating tumour DNA and other clinical factors to determine patient's outcome. There is scope to integrate biomarkers in treatment decision algorithms aiming to make personalised treatment modifications (e.g. decision to treat with immunotherapy or not). VIGILANCE is a highly exploratory observational study to understand how these biomarkers might inform a future hypothesis driven interventional study.