RecruitingPhase 2Diagnostic testctDNA to Predict Response to Chemo-Immunotherapy and Detect Minimal Residual Disease in Non-Small Cell Lung CancerThe purpose of this study is to determine if a blood test called circulating tumor DNA (ctDNA) can be used to predict how well patients will respond to treatment and if there is any cancer left after surgery. The investigators will also study if a drug called pembrolizumab can help prevent the cancer from coming back in patients who are ctDNA-positive or who have evidence of cancer after treatment and surgery.