This clinical trial is focused on studying a type of skin cancer known as Stage II Melanoma, which has been surgically removed but is considered high-risk for returning. The study is comparing two treatments: a medication called Pembrolizumab (also known by its code name MK-3475) and a placebo. Pembrolizumab is a type of drug that is given through an intravenous infusion, which means it is delivered directly into the bloodstream through a vein. It is designed to help the body’s immune system fight cancer cells.

The purpose of this study is to see if Pembrolizumab can help prevent the cancer from coming back after surgery. Participants in the study will be randomly assigned to receive either Pembrolizumab or a placebo. The study will be conducted over a period of time, and participants will receive regular infusions and follow-up care to monitor their health and the status of their cancer. The main goal is to compare how long participants remain free from cancer recurrence between the two groups.

Throughout the study, researchers will also look at other important outcomes, such as how long participants live without the cancer spreading to other parts of the body, overall survival rates, and any side effects experienced. This information will help determine the effectiveness and safety of Pembrolizumab as a treatment option for high-risk Stage II Melanoma.