An immunotherapy is a treatment for a disease that works by manipulating a patient's immune system. Depending on the disease, an immunotherapy might induce, enhance, or suppress immune response. Vaccines, for example, train the immune system to attack certain kinds of cells. Immunosuppresant drugs can be used to treat unpleasant immune response caused by allergens. In the context of cancer, immunotherapies can be used to encourage a patient's immune system to attack cancerous cells.
Because cancerous cells are extremely similar to a patient's healthy cells, they are often tolerated by the immune system. Even when they are unusual enough to be identified by the body, cancer cells can gradually suppress or evade immune response. Cancer immunotherapies enable the immune system to recognize and destroy cancerous cells that it otherwise could not. Immunotherapy has been a major area of drug development over the last decade and has produced significant advances in treating some forms of cancer.