Immunotherapy is a treatment that uses the body's immune system to fight cancer. 

The immune system is made up of cells, organs and proteins that help defend the body from infections and other diseases. Immunotherapy can stimulate or strengthen the immune system's natural defenses so that they attack cancer cells more intensely or effectively. It may also use substances made by the body or in a laboratory to improve the immune response to cancer.

Immunotherapy can treat many types of cancer, either alone or in combination with other treatments, such as chemotherapy.