Immunotherapy for Cancer: How It Works and What to Expect

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Immunotherapy is a cancer treatment that boosts your immune system so it is better at finding and destroying cancer cells. Unlike chemotherapy, which uses toxic drugs, it trains your own immune cells to target cancer more effectively, which can mean longer survival and fewer side effects for some people [1].

Quick Answer: What is immunotherapy for cancer?

Immunotherapy is a type of cancer treatment that boosts or trains the body's natural defenses to recognize and attack cancer cells. Common types include checkpoint inhibitors, CAR T-cell therapy, monoclonal antibodies and cancer vaccines. It often has fewer side effects than chemotherapy, but it does not work for every cancer or person, and only some people have long-lasting remissions. [1]

What the research says

• Some people with advanced melanoma live much longer with checkpoint inhibitors. In a randomized trial of previously untreated advanced melanoma, overall survival at 5 years was 52% with nivolumab plus ipilimumab and 44% with nivolumab alone, compared with 26% with ipilimumab alone (hazard ratio for death 0.52 and 0.63 versus ipilimumab). No sustained decline in quality of life was seen with the nivolumab-containing regimens (Larkin et al., New England Journal of Medicine, 2019 [2]).

• Only a minority of all patients with cancer actually respond. A US cross-sectional estimate based on public data found that the share of patients with cancer eligible for checkpoint inhibitors rose from 1.54% in 2011 to 43.63% in 2018, while the share estimated to respond was 12.46% in 2018. The authors called this improvement real but modest and urged research into biomarkers to predict who benefits (Haslam & Prasad, JAMA Network Open, 2019 [3]).

• Side effects are common, but most are not severe. A meta-analysis of 125 trials of single-agent PD-1 and PD-L1 inhibitors (20,128 patients) found that 66.0% of patients had at least one treatment-related adverse event of any grade, and 14.0% had one of grade 3 or higher. The most common were fatigue (18.26%), itching (10.61%) and diarrhea (9.47%) (Wang et al., JAMA Oncology, 2019 [4]).

Understanding Immunotherapy

Immunotherapy marks a shift in cancer care: instead of relying only on toxic drugs, it builds on the body's natural ability to protect itself. The goal is to strengthen the immune system's patrol so it can find and kill cancer cells that would otherwise go undetected [1].

How Immunotherapy Works

Your immune system protects you from threats ranging from allergens and germs to cancer cells, but cancer cells are often good at hiding from these defenses. Immunotherapy helps by [1]:

• Training immune cells to recognize specific markers on cancer cells.

• Boosting the production of cancer-fighting immune cells.

• Preventing cancer cells from sending signals that turn off the immune response.

Feature	Immunotherapy	Chemotherapy
Mechanism	Uses the body's immune system	Uses toxic drugs to kill cells
Targeting	Highly targeted to cancer markers	Attacks all rapidly dividing cells
Side effects	Often fewer and less severe	Can be severe and widespread
Primary goal	Train the immune system to fight	Directly destroy tumor cells

Primary Types of Immunotherapy

There are several categories of immunotherapy, each using a different biological mechanism to fight cancer [1].

Checkpoint Inhibitors

Checkpoint inhibitors are drugs that help T cells, a type of white blood cell, keep fighting cancer for longer. Normally, the body uses checkpoint proteins to tell T cells when to switch on or stand down, which keeps them from overreacting and damaging healthy tissue. Cancer cells can exploit these checkpoints to turn T cells off. Checkpoint inhibitors block that signal, so the T cells keep attacking [1].

How a checkpoint inhibitor works: blocking the “off” signal lets T cells attack the cancer cell.

Adoptive Cell Therapy

Also called T-cell transfer therapy, this approach changes a patient's own immune cells in a laboratory [1]:

• CAR T-cell therapy: T cells are removed, modified so they make a protein called CAR that helps them fight cancer, and returned to the patient.

• Tumor-infiltrating lymphocytes (TIL): T cells are removed from inside a tumor and tested to find the best cancer fighters, then copied in large numbers and returned to the body.

Monoclonal Antibodies and Cancer Vaccines

Monoclonal antibodies are lab-made proteins that can block signals cancer cells need to grow, flag cancer cells for destruction, or deliver toxic or radioactive material directly into them. Cancer vaccines used as immunotherapy are different from vaccines that prevent infections: they do not prevent cancer, but train the immune system to recognize identifying markers on cancer cells you already have [1].

Immune System Modulators

Immune system modulators boost the immune response in many different ways. They include cytokines, which help immune cells coordinate attacks, and Bacillus Calmette-Guérin (BCG), which is used after surgery to stimulate the immune system against bladder cancer cells [1].

Administration and Cycles

Immunotherapy can be given alone or together with other cancer treatments. The method depends on the cancer type and the specific drug [1]:

• Intravenous (IV): infusions delivered into a vein.

• Oral: pills or capsules taken by mouth.

• Topical: creams or ointments applied to the skin (common for early-stage skin cancer).

• Injection: shots that target the tumor or diseased area.

• Intravesical: BCG delivered directly into the bladder.

Treatment may happen daily, weekly, monthly, or in cycles that include a period of active treatment followed by a rest period. The break gives your body time to produce new, healthy cells [1].

Common ways immunotherapy is given: IV infusion, oral pills, topical cream, and injection into the bladder.

Benefits and Potential Risks

Immunotherapy is one of the most promising developments in cancer care, but it is not a universal cure and it carries its own risks [1].

Key Benefits

The biggest advantage is that it can help some people with advanced or recurring cancers live longer. Because it targets cancer cells more specifically than chemotherapy, many people have less damage to healthy tissue and fewer side effects [1].

Potential Risks and Side Effects

Side effects range from mild to severe and depend on the specific drug and your overall health. In some cases the immune system begins to attack healthy organs, which needs urgent medical care. Cancer cells can also develop new ways to evade the immune system, so treatment may lose effectiveness over time [1].

Side effect level	Common symptoms	Management
Mild	Fatigue, skin rash, fever	Monitoring and supportive care, after checking with your care team
Moderate	Diarrhea, joint pain, cough	Prescription medication and rest
Severe	Organ inflammation, breathing issues	Immediate medical attention

Because immune-related side effects can escalate, tell your oncology team about any new symptom rather than waiting to see if it becomes severe.

A patient guide to common immunotherapy side effects and the warning signs that need immediate medical attention.

When to Call Your Oncologist

Call your oncology team if you have side effects during or after treatment that are more serious than expected, and whenever you have questions about your treatment. Useful questions to ask include [1]:

• How will I receive immunotherapy, and how long will each session and the whole course take?

• What short-term and long-term side effects should I know about?

• Are there newer forms of immunotherapy available to me through clinical trials?

• How will immunotherapy affect my outlook, and how will we know whether it is working?

Bottom Line

Immunotherapy has changed cancer care by putting the body's own defenses to work against tumors. For some people with advanced cancers it brings longer survival and gentler treatment than chemotherapy, but it works for only a minority of patients overall, it can cause serious immune-related side effects, and cancer can eventually adapt to it. Ongoing research continues to expand the cancers it can treat and to improve results [1].

Your next step: if you or a loved one are exploring cancer treatment options, ask an oncologist whether immunotherapy could be a suitable part of your care plan, and ask about current clinical trials.

Frequently Asked Questions

What is the main difference between immunotherapy and chemotherapy?

Immunotherapy uses your own immune system to target cancer, whereas chemotherapy uses toxic drugs that directly kill rapidly dividing cells, including some healthy ones. This often makes immunotherapy more targeted, with potentially fewer side effects.

Can immunotherapy cure cancer?

Current immunotherapies are not considered a definitive cure, but they can help some people with cancer live longer. In one large trial in advanced melanoma, 52% of patients on combination immunotherapy were alive at five years.

How long does immunotherapy treatment take?

The duration varies widely. Some people receive treatment daily or weekly, while others follow a cycle with rest periods. The total length depends on how the cancer responds and the specific drug used.

Is immunotherapy effective for all types of cancer?

No. Immunotherapy does not work for every type of cancer or every person. It is most often recommended for cancers that have spread, come back after treatment, or have not responded to other therapies.

What are the most common side effects of immunotherapy?

Common side effects include fatigue, skin rash or itching, diarrhea, fever, and flu-like symptoms. They are often milder than chemotherapy side effects, but they can become severe if the immune system attacks healthy tissues.

How is immunotherapy administered?

Immunotherapy can be given intravenously (IV), as pills by mouth, as creams applied to the skin, by injection into a tumor or diseased area, or directly into the bladder (intravesical).

What are checkpoint inhibitors?

Checkpoint inhibitors are a type of immunotherapy that stops cancer cells from sending “off” signals to T cells, so the immune system can keep fighting the cancer.

What is CAR T-cell therapy?

CAR T-cell therapy is a form of adoptive cell therapy in which a patient's T cells are removed, genetically modified in a lab to better recognize and attack cancer cells, and then returned to the body.

Can cancer become resistant to immunotherapy?

Yes. Cancer cells are highly adaptable and can develop new ways to hide from or suppress the immune system, which may cause the treatment to stop working over time.

When should I contact my doctor during treatment?

Contact your oncology team right away if you have severe side effects such as difficulty breathing, intense diarrhea, or signs of organ inflammation, or if you have questions about your progress.

Related Reading

Neoadjuvant Therapy: Types, Uses and Benefits explains neoadjuvant cancer therapy.

BiTE Therapy (Bispecific T-Cell Engagers): How It Works and Side Effects explains BiTE immunotherapy.

BCG Treatment for Bladder Cancer: Procedure, Schedule and Side Effects explains BCG treatment for bladder cancer.

Adjuvant Therapy: What It Is, Types and Why It's Used explains adjuvant cancer therapy.

Biologics: What They Are, Types, Uses and Side Effects explains biologic medicines and how they're used.

References

1. Cleveland Clinic. Immunotherapy. Cleveland Clinic. August 12, 2025. https://my.clevelandclinic.org/health/treatments/11582-immunotherapy

2. Larkin J, Chiarion-Sileni V, Gonzalez R, et al. Five-year survival with combined nivolumab and ipilimumab in advanced melanoma. New England Journal of Medicine. 2019;381(16):1535-1546. PMID 31562797. https://doi.org/10.1056/NEJMoa1910836

3. Haslam A, Prasad V. Estimation of the percentage of US patients with cancer who are eligible for and respond to checkpoint inhibitor immunotherapy drugs. JAMA Network Open. 2019;2(5):e192535. PMID 31050774. https://doi.org/10.1001/jamanetworkopen.2019.2535

4. Wang Y, Zhou S, Yang F, et al. Treatment-related adverse events of PD-1 and PD-L1 inhibitors in clinical trials: a systematic review and meta-analysis. JAMA Oncology. 2019;5(7):1008-1019. PMID 31021376. https://doi.org/10.1001/jamaoncol.2019.0393

Medical disclaimer

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. The clinical information in this guide reflects source material last reviewed in August 2025.