A natural substance that helps the body’s immune system fight infection and other diseases, such as cancer. Interferons are made in the body by white blood cells and other cells, but they can also be made in the laboratory to use as treatments for different diseases. In cancer therapy, interferons may help keep cancer cells from growing and may help kill cancer cells. There are three main types of interferons: interferon-alfa, interferon-beta, and interferon-gamma. An interferon is a type of cytokine and type of immunomodulating agent.