This clinical trial is focused on studying treatments for Non-Small Cell Lung Cancer (NSCLC), a common type of lung cancer. The study will explore the effectiveness of a combination of treatments, including pembrolizumab (also known as Keytruda) and a new investigational treatment called mRNA-4157. Pembrolizumab is a medication that helps the immune system fight cancer, while mRNA-4157 is a new type of treatment being tested for its potential to improve outcomes in cancer therapy. The study will also involve a comparison with a placebo, which is a substance with no active medication.

The purpose of the study is to compare the effects of the combination of mRNA-4157 and pembrolizumab with pembrolizumab alone in patients with resectable Stage II to IIIB NSCLC who have not achieved a complete response after initial treatment. Participants will receive these treatments through intravenous infusion, which means the medication is given directly into a vein. The study will last for a period of up to 42 weeks, during which participants will be monitored for their response to the treatment and any side effects they may experience.

Throughout the study, researchers will assess various outcomes, including how long patients remain free of cancer, overall survival rates, and the quality of life of participants. The study aims to provide valuable information on whether the addition of mRNA-4157 to pembrolizumab can offer better results for patients with NSCLC. This research is part of ongoing efforts to find more effective treatments for lung cancer and improve the lives of those affected by this disease.