Additional Study Information: This study is aimed at finding patients who have small amounts of cancer DNA in their blood (called circulating tumor DNA or ctDNA) after surgery. This may indicate that you have minimal residual disease (MRD), meaning that even after surgery, there are still some remaining cancer cells releasing cancer DNA into your bloodstream. MRD after surgery may mean that the risk of cancer coming back is higher, which is why we would like to give additional treatment after your tumor has been removed. The study is focusing on subjects with stage II-III non-small cell lung cancer (NSCLC) that is being treated/has already been treated by removing it through surgery. This study will also investigate the safety of this new drug combination. Some patients will get durvalumab and chemotherapy and other patients will get a placebo and chemotherapy to see which prevents their lung cancer from coming back better.