This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on July 20, 2022.

Immunotherapy is a broad category of cancer therapies that triggers the body's immune system to fight cancer cells. Cancer cells are different from normal cells, in that they do not die normally. They rapidly divide like an out-of-control copy machine that won't stop creating images.

These abnormal cells frequently change, or mutate, helping them evade the immune system, which protects the body from disease and infections. Cancer immunotherapy drugs are designed to alert the immune system about these mutated cells so it can locate and destroy them.

To help answer patients' questions about immunotherapy and when it may be used as part of a cancer treatment regimen, this guide will cover:

How does the immune system work?

A key function of the immune system is to distinguish normal cells in the body from foreign cells.

The immune system is always on patrol, like a police force charged with ridding the body of foreign invaders, such as viruses, bacteria or fungi. Lymph nodes, which make up most of the immune system, serve as police stations throughout the body. White blood cells, including lymphocytes such as “T cells,” fight infection and cancer. They are the police officers. When a foreign invader is detected, the entire immune system is alerted through chemical signals, just as a police station would radio police officers to alert them about a problem.

The immune system relies on receptor proteins on certain immune cells to detect the invaders. At certain checkpoints, when activated or deactivated, these receptors allow it to distinguish between healthy and invading cells. The checkpoints are needed to keep the immune system from attacking healthy cells.

Cancer cells don't trigger an immune response because they are the body’s own cells that have mutated—so those once-healthy cells no longer behave like normal cells. Because the immune system doesn’t recognize the distinction, these dangerous cells can continue to grow, divide and spread throughout the body.

How does immunotherapy work to fight cancer?

Immunotherapies use different methods to attack tumor cells. Immunotherapy types fall into three general categories:

Checkpoint inhibitors, where cancer cell signals that trick the immune system into thinking they’re healthy cells are disrupted, exposing them to attack by the immune system

Cytokines, which are protein molecules that help regulate and direct the immune system that are synthesized in a laboratory and then injected into the body in much larger doses than are produced naturally

Cancer vaccines, which may reduce the risk of cancer by attacking viruses that cause cancer, or may treat cancer by stimulating the immune system to attack cancer cells in a specific part of the body

Immunotherapy may be used alone or in combination with other cancer treatments, such as surgery, chemotherapy, radiation therapy and targeted therapy.

What are some of the immunotherapy drugs?

Current checkpoint inhibitor drugs target the PD-1 and the CTLA-4 receptors. Common checkpoint inhibitors include:

  • Ipilimumab (Yervoy®)
  • Pembrolizumab (Keytruda®)
  • Nivolumab (Opdivo®)
  • Atezolizumab (Tecentriq®)

Common cytokines used in cancer therapy include:

  • Interleukin-2 (IL-2)
  • Interferons-alpha (IFN-alpha)

New immunotherapy drugs continue to be developed.

How are immunotherapy drugs given?

The method of administration for immunotherapy drugs differs depending on the specific medication selected, but the most common administration routes are those listed below:

Oral: Capsules or pills taken by mouth

Intravenous: Drugs that are administered through one of the patient's veins

Intravesical: Drugs administered into a patient's bladder

Topical: Drugs that come in a lotion or cream that the patient applies to the skin

Tumor-agnostic therapies

The U.S. Food and Drug Administration has also approved immunotherapy to treat cancers with specific genetic features, regardless of where in the body they originate. These treatments, called tumor-agnostic therapies, may be used to treat these malignancies:

Solid tumors with microsatellite instability-high (MSI-h) or mismatch repair deficiency (dMMR): These tumors may have unstable strands of DNA or are unable to repair DNA damage.

Solid tumors with high tumor mutation burden (TMB-h): These tumors have cells with a high number of different gene mutations, which may make them more likely to respond to immunotherapy.

Signs immunotherapy is working

After immunotherapy is given, the care team looks for signs that the drugs are working. Typically, the most important sign that the medication works is that the tumor is either getting smaller or is remaining stable without an increase in size. 

Some patients believe that experiencing side effects is an indication that immunotherapy is working, but not all patients with successful immunotherapy treatment experience side effects from the drugs.

What are immunotherapy side effects?

Immunotherapy may cause a variety of side effects—many are flu-like symptoms—including:

  • Fatigue
  • Nausea or vomiting
  • Mouth sores
  • Diarrhea
  • High blood pressure
  • Fluid buildup, usually in the legs
  • Fever or chills
  • Pain or weakness
  • Headaches
  • Rashes or itching

The side effects of immunotherapy generally become less severe after the first treatment.

Throughout treatment, the care team provides supportive care services, including nutritional support, naturopathic support, pain management, oncology rehabilitation, behavioral health and spiritual support. These therapies may help reduce side effects and improve the patient's overall quality of life during immunotherapy.

Types of immunotherapy

The goal of immunotherapy is to try to reset the body’s immune system to once again be able to find and attack cancer cells. The many types of immunotherapies work differently and have their own risks and benefits. Which of these treatments the care team recommends depends on the type of cancer and its stage.

Monoclonal or therapeutic antibodies are grown in a lab and injected into the body. Some mark cancer cells so the immune system is able to recognize and destroy them. Others are more direct in their approach, stopping the growth of cancer cells or causing their self-destruction.

CAR T-cell therapy goes by many names—including adoptive cell therapy, adoptive immunotherapy or immune cell therapy. Essentially, the care team harvests white blood cells from inside the tumor and grows them in a lab, making changes to strengthen their natural ability to fight cancer. These cells are grown in large batches and injected back into the body to fight the cancer.

Immune checkpoint inhibitors are a type of drug that removes natural blockades within the body that keep the immune system in check. Without these natural blockades, it may overreact—like in autoimmune diseases. But cancer cells often use these blockades, or proteins, to hide from the immune system. With these blockades deactivated through checkpoint inhibitors, the door is opened, and the body is able to respond more strongly to the cancer cells.

Cancer vaccines, sometimes called immunotherapeutic or treatment vaccines, boost the immune system response when the patient already has cancer. They aren’t preventative vaccines like those for viruses, such as the flu. By providing immune cells with a target found on cancer cells, they prime the body to create antibodies to attack cancer cells. Vaccines usually contain an immune-stimulating agent to rally the white blood cell troops specifically against that protein target.

Cytokines are proteins created by the body during natural infections that play an important role in stimulating the immune system cells. By supplementing the body’s natural cytokines with versions created in laboratories, these treatments help ramp up immune cells and move them toward their target: the tumor.

Immune system modulators, sometimes called immunomodulators, are drugs that ramp up the body’s immune reaction. Different immunomodulators act in different ways—some focus specifically on certain parts of the immune system, while others act across the whole body.

Immunotherapy may be given as an IV medication into the vein, an oral medication in pills or capsules, or even a topical medication on the skin.

Immunotherapy vs. chemotherapy

Both immunotherapy and chemotherapy are commonly used cancer treatments that use drugs to stop or slow the growth of cancerous cells. However, while chemotherapy drugs are used to attack rapidly producing cells throughout the body, immunotherapy triggers the immune system’s ability to identify and attack cancer cells.

The side effects can be very different between chemotherapy and immunotherapy, too. Because chemotherapy can’t differentiate between the cells it’s targeting, it affects both fast-growing cancerous and fast-growing normal cells, like those responsible for hair and skin growth and those lining the digestive tract and forming bone marrow. That why side effects like hair loss, nausea and vomiting, and skin and nail changes are more common and sometimes more severe with chemotherapy.

Benefits of immunotherapy

Overall, immunotherapies are still less common than surgery or chemotherapy to treat cancer. But for some types of cancer, these therapies are now an important treatment option. Many other immunotherapies are still in clinical trials.

Immunotherapies have the potential to be more comprehensive and less toxic than other types of treatments for cancer, because they harness the power of the body itself to attack the tumor instead of introducing chemicals into the body.

Immunotherapies are a very active area of research in cancer therapy, and new treatments continue to be approved.

Risks of immunotherapy

Risks vary by the type of immunotherapy, the type of cancer, the stage, a patient’s general health and current treatment regimen. Every treatment has different side effects, and patients may respond differently to the same treatment.

Generally, side effects may result when a patient's immune system ramps up to function on “high.” As when a patient gets a vaccine, he or she may experience flu-like symptoms—including fever, chills, weakness, dizziness, nausea, muscle aches, fatigue or headache—because the immune system is doing its job.

These treatments may cause high levels of inflammation in healthy cells and tissues and side effects from that response, such as a skin rash. Steroids may treat the side effects from that inflammation—but steroids also have some side effects of their own.

Some people develop resistance to immunotherapy. Rarely, doctors have observed severe or even fatal allergic and inflammatory reactions to some types of immunotherapy.

The patient's body may or may not respond to immunotherapy. Only some people receiving these treatments respond to them. Researchers are working on better understanding the common link between people who do respond and why.

Ask the care team about the risks and benefits of immunotherapy for the patient's type and stage of cancer.

What is the success rate for immunotherapy

Between 20 percent and 40 percent of patients who are given immunotherapy mount a response to the drugs.

Who is a candidate for immunotherapy?

Members of the patient's multidisciplinary care team work together to develop treatment options tailored to each patient’s individual cancer care needs. Immunotherapy treatment may be an option for patients who have certain types of cancer. The treatment may work better for some types of cancer than others, so the patient's oncologist would closely monitor his or her progress and may recommend immunotherapy be used in combination with other treatments.

Once the care team develops a recommended treatment plan, members spend the time necessary with the patient and his or her caregiver to explain each option, its potential risks and benefits, side effects and other essentials. Then the patient and his or her care team work together to decide which immunotherapy or other treatment options are right for him or her, allowing for informed decisions about the care plan.

Many patients come to City of Hope to get a better understanding of their cancer diagnosis or treatment plan. Our cancer experts have access to a wide range of diagnostic tools and comprehensive treatment options, including genomic testing, immunotherapy, targeted therapy and clinical trials. We also offer a personalized approach to cancer care and a team of multidisciplinary experts to help patients prevent or manage the side effects of cancer treatment.

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Show references
  • National Cancer Institute (2019, September 24). Immunotherapy for Cancer.
  • American Cancer Society (2019, December 27). Cytokines and Their Side Effects.
  • American Cancer Society (2019, December 27). How Immunotherapy Is Used to Treat Cancer.
  • National Cancer Institute (2023, February 16). Side Effects of Immunotherapy.
  • U.S. National Library of Medicine, ClinicalTrials.gov.
  • Nature Portfolio. Decoding the signs of response to cancer immunotherapy.