This type of therapy uses the body's natural ability (immune system) to fight disease or protect the body from treatment side effects. Immunotherapy is designed to repair, stimulate or enhance the immune system's natural anticancer function, assisting it to recognize cancer cells in the body and work to eliminate them. Another approach is to remove cancer cells from the body and alter them genetically to elicit a strong immune response. These cells then can be returned to the body in the hope that they will act as a cancer vaccine. A variety of clinical trials using this approach are currently under way.

Researchers are testing several types of immunotherapy, alone or in conjunction with other treatments. Immunotherapy may be used when colorectal cancer has spread to other organs or when the cancer has recurred. Most of these treatments are given by injection.