Cancer immunotherapy is the use of the immune system to treat cancer.

Immunotherapies are often categorized as active, passive, or combinatory (active and passive). These immunotherapeutic approaches exploit the fact that cancer cells often have subtly different molecules on their surface that can be detected by the immune system known as cancer antigens; cancer antigens are often proteins or other macromolecules (e.g., carbohydrates).

Active immunotherapy is used to provoke the immune system into attacking the tumor cells by targeting tumor-associated antigens (TAAs).
Passive immunotherapies are intrinsically functional and include monoclonal antibodies, lymphocytes, and cytokines. Among these, antibody therapies are the most successful to date and treat a wide range of cancers. Antibodies are proteins produced by the immune system that bind to a target antigen on the cell surface. In normal physiology the immune system uses them to fight pathogens. Each antibody is specific to one or a few proteins. Those that bind to cancer antigens are used to treat cancer. Cell surface receptors are common targets for antibody therapies and include the CD20, CD274, and CD279. Once bound to a cancer antigen, antibodies can induce antibody-dependent cell-mediated cytotoxicity, activate the complement system, or prevent a receptor from interacting with its ligand, all of which can lead to cell death. Multiple antibodies are approved to treat cancer, including alemtuzumab, ipilimumab, nivolumab, ofatumumab, and rituximab.

Active cellular therapies usually involve the removal of immune cells from the blood or from a tumor. Immune cells specific for the tumor are activated, cultured, and returned to the patient where the immune cells attack the cancer. Cell types that can be used in this way are natural killer cells, lymphokine-activated killer cells, cytotoxic T cells, and dendritic cells.

Interleukin-2 and interferon-α are cytokines, proteins that regulate and coordinate the behavior of the immune system. They have the ability to enhance antitumor activity and thus can be used as passive cancer treatments. Interferon-α is used in the treatment of hairy-cell leukemia, AIDS-related Kaposi's sarcoma, follicular lymphoma, chronic myeloid leukemia, and malignant melanoma. Interleukin-2 is used in the treatment of malignant melanoma and renal cell carcinoma.

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Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on January 18, 2016.