Interferons are cytokines, naturally produced proteins of the immune system. When immune cells are activated, they will begin to produce interferons and other natural immune-signaling substances. These substances not only combat foreign cells which may cause infection, but can also prevent the growth and spread of other diseased cells, including cancer.

Exactly how interferons work is not clear. It is believed they shine a spotlight on the antigens found on tumor cells, alerting large numbers of immune system T cells to attack the tumor. Interferons may also inhibit tumor growth by attacking the blood vessels that feed cancer cells.

Of the three major types of interferons produced by the body, only one, interferon alpha, has been found to be useful in treating cancers, including melanoma. Interferon alfa-2a and interferon alfa-2b are synthetic versions of interferon alpha.