Nivolumab is primarily used in the treatment of various types of cancer. It works by enhancing the body's immune system to fight cancer cells. Specifically, it is approved for treating melanoma, non-small cell lung cancer, renal cell carcinoma, Hodgkin lymphoma, and head and neck squamous cell carcinoma. Nivolumab targets the PD-1 receptor on T cells, blocking its interaction with PD-L1 and PD-L2, which are often expressed by cancer cells to evade immune detection. This mechanism helps to restore the immune system's ability to attack and destroy cancer cells. It is often used when other treatments have failed or in combination with other therapies to improve outcomes. Regular monitoring is required during treatment to manage potential immune-related side effects.