Immunotherapy is a type of biological therapy that uses substances to stimulate or suppress the immune system to help the body fight cancer, infection, and other diseases. Some types of immunotherapy only target certain cells of the immune system.

The field is emerging as one of the most promising approaches to cancer treatment, and immunotherapy is now widely recognized as a fourth option—with surgery, radiation and chemotherapy. It is increasingly becoming an integral component for the treatment of a number of cancers.

The National Cancer Institute provides an overview of how the immune system can be used to treat cancer.