The immune system protects the body from infection. It does this by detecting germs such as bacteria or viruses and making proteins that fight infection. These proteins are called antibodies.

Scientists can make special antibodies in a lab that seek out cancer cells instead of bacteria. Called monoclonal antibodies, they are also a type of targeted therapy.

Some monoclonal antibodies work by sticking to cancer cells. This makes it easier for other cells made by the immune system to find, attack, and kill the cells.

Other monoclonal antibodies work by blocking signals on the surface of the cancer cell that tell it to divide leading the tumor to grow.

Another type of monoclonal antibody carries radiation or a chemotherapy drug to cancer cells. These cancer-killing substances are attached to the monoclonal antibodies, which then deliver the toxins to the cancer cells.

Monoclonal antibodies are now used to treat most types of cancer.

"Checkpoints" are specific molecules on certain immune cells that the immune system either turns on or turns off to create an immune response. Cancer cells can use these checkpoints to avoid being attacked by the immune system.

Immune checkpoint inhibitors are a newer type of monoclonal antibody that act on these checkpoints to boost the immune system so it can attack cancer cells.

PD-1 and PD-L1 inhibitors are used to treat a variety of different cancer types.

Drugs that target CTLA-4 treat melanoma of the skin, kidney cancer, lung cancer, and other cancer types.

These therapies boost the immune system in more general way than monoclonal antibodies. There are two main types:

Interleukin-2 (IL-2) helps immune cells grow and divide more quickly. A lab-made version of IL-2 is used for advanced forms of kidney cancer and melanoma.

Interferon alpha (INF-alfa) makes certain immune cells better able to attack cancer cells. It is rarely used to treat:

• Hairy cell leukemia
• Chronic myelogenous leukemia
• Follicular non-Hodgkin lymphoma
• Cutaneous (skin) T-cell lymphoma
• Kidney cancer
• Melanoma
• Kaposi sarcoma

This type of therapy uses viruses that have been altered in a lab to infect and kill cancer cells. When these cells die, they release substances called antigens. These antigens tell the immune system to target and kill other cancer cells in the body.

This type of immunotherapy is currently used to treat melanoma.

The side effects for different types of immunotherapy for cancer differ by the type of treatment. Some side effects occur where the injection or IV enters the body, causing the area to be:

• Sore or painful
• Swollen
• Red
• Itchy

Other possible side effects include:

• Flu-like symptoms (fever, chills, weakness, headache)
• Nausea and vomiting
• Diarrhea
• Muscle or joint aches
• Feeling very tired
• Headache
• Low or high blood pressure
• Inflammation of the liver, lungs, endocrine organs, gastrointestinal tract, or skin

These therapies can also cause a severe, sometimes fatal, allergic reaction in people sensitive to certain ingredients in the treatment. However, this is very rare.

Biological therapy; Biotherapy

National Cancer Institute website. CAR T cells: engineering patients' immune cells to treat their cancers. www.cancer.gov/about-cancer/treatment/research/car-t-cells. Updated March 10, 2022. Accessed June 13, 2024.

National Cancer Institute website. Immunotherapy to treat cancer. www.cancer.gov/about-cancer/treatment/types/immunotherapy. Updated September 24, 2019. Accessed June 13, 2024.

Tseng D, Schultz L, Pardoll D, Mackall C. Cancer immunology. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff's Clinical Oncology. 6th ed. Philadelphia, PA: Elsevier; 2020:chap 6.

Updated by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.