This clinical trial is focused on studying a type of lung cancer known as Non-small Cell Lung Cancer (NSCLC), specifically in stages II, IIIA, and certain cases of stage IIIB. The study is investigating the effects of a treatment called Pembrolizumab, also known by its code name MK-3475, which is used in combination with chemotherapy drugs. The chemotherapy drugs involved in this study include Cisplatin, Gemcitabine, and Pemetrexed. These treatments are given to patients who have a type of lung cancer that can be surgically removed.

The purpose of the study is to see how well these treatments work when given before and after surgery. Some participants will receive the combination of chemotherapy and Pembrolizumab, while others will receive chemotherapy with a placebo. The study will monitor participants over a period of time to assess their recovery and overall health outcomes.

Participants will receive the treatments through an intravenous infusion, which means the medication is delivered directly into the bloodstream through a vein. The study will track important outcomes such as how long participants live without the cancer returning and their overall survival. Additionally, the study will look at the response of the cancer to the treatment and any side effects experienced by the participants. The trial aims to provide valuable information on the effectiveness of adding Pembrolizumab to standard chemotherapy for treating this type of lung cancer.