This study is for patients that have been diagnosed with stage III-IV Melanoma after a complete resection (no evidence of disease). The investigational drug in this study is relatlimab in combination with nivolumab. Investigational means the drug is not approved by the United States Food and Drug Administration (US FDA). Participants will be assigned to receive relatlimab with nivolumab in a fixed dose combination (FDC, both drugs in a single vial) or nivolumab alone, administered by intravenous (IV) infusion, meaning the drug is a solution given through a vein. The infusion is planned to take 30 minutes. Neither the participants or study doctor will know what is being administered.

This study is designed to explore if treating stage III-IV resectable melanoma patients with this combination, after they have surgery to remove all tumors, will reduce the probability of having progressive disease when compared to nivolumab alone, as well as to assess the possible side effects that this combination therapy might have. Participants can expect to be on this study for a minimum of 6 years.

This study is for older adults with colorectal cancer. The purpose is to determine if low muscle mass plays a role in side effects from chemotherapy.

This study is for patients that have been diagnosed with Merkle Cell Carcinoma. The investigational drug in this study is pembrolizumab. The purpose of this study is to compare the usual approach of post-surgery observation with or without radiation to using pembrolizumab with or without radiation after surgery. Participants can expect to be on this study for a total of 5 years.