This clinical trial is focused on studying treatments for stage IV Non-Small Cell Lung Cancer (NSCLC), a type of lung cancer that has spread to other parts of the body. The study is evaluating the effectiveness of a medication called pembrolizumab, which is also known by the brand name Keytruda. Pembrolizumab is a type of immunotherapy, which means it helps the body’s immune system fight cancer. In this trial, pembrolizumab may be used alone or in combination with another medication called pemetrexed, which is a chemotherapy drug. The study will also compare these treatments to a placebo, which is a substance with no active medication, to see how well they work in controlling the disease.

The purpose of the study is to determine how effective pembrolizumab is when used as a maintenance treatment after an initial six months of chemotherapy combined with pembrolizumab. The chemotherapy used in the initial treatment includes drugs like carboplatin, cisplatin, and paclitaxel, which are common medications used to treat various cancers. The study will observe patients to see if continuing pembrolizumab helps in maintaining disease control compared to stopping treatment after the initial phase.

Participants in the study will receive treatment through infusions, which means the medication is given directly into the bloodstream. The study will last for several months, and patients will be monitored regularly to assess their response to the treatment. The goal is to find out if pembrolizumab can help patients live longer and maintain a better quality of life compared to those who do not continue with the treatment after the initial phase. The study will also look at how the treatment affects different subtypes of NSCLC, such as squamous and non-squamous cell carcinoma, and how it relates to specific tumor characteristics like PD-L1 expression, which is a protein that can affect how the immune system responds to cancer.