Immunotherapy is a broad category of cancer therapies that use the body’s immune system to fight cancer cells. These cells are different from normal cells, in that they do not die normally. Think of these rapidly-dividing cells like an out-of-control copy machine that won’t stop creating images. These abnormal cells frequently change, or “mutate,” to evade the immune system. Immunotherapy drugs are designed to alert the immune system about these mutated cells so it can locate and destroy them.