Cancer Immunotherapy: How It Works and Common Side Effects

Your oncologist has suggested immunotherapy. You may have heard it described as a breakthrough, and you may also have heard that its side effects are different from chemotherapy. Both are true. This guide explains how immunotherapy works, which side effects to watch for, and when to call your team.

How immunotherapy works

Your immune system protects you from germs and also removes some abnormal cells. Cancer cells often find ways to hide from the immune system or to switch it off. Immunotherapy helps the immune system see and attack cancer again. [1]

This is different from chemotherapy, which attacks fast-growing cells directly. Immunotherapy works through your own immune cells.

Main types

• Immune checkpoint inhibitors: drugs that release the "brakes" on immune cells called T cells. These are the most widely used type. [2]
• CAR T-cell therapy: your own T cells are collected, changed in a lab so they can find a target on cancer cells, then given back to you. It is used mainly for some blood cancers. [1]
• Other types: some monoclonal antibodies, cancer vaccines, and immune system modulators. [1]

Checkpoint inhibitors

Checkpoints are proteins that stop the immune system from attacking healthy cells. Some cancer cells use these checkpoints to escape. Checkpoint inhibitors block them. [2]

• PD-1 inhibitors, such as pembrolizumab and nivolumab.
• PD-L1 inhibitors, such as atezolizumab and durvalumab.
• CTLA-4 inhibitors, such as ipilimumab.

These drugs are used for many cancers, including melanoma, lung, kidney, bladder, and some head and neck cancers. They are usually given by IV every few weeks. Some people receive two checkpoint inhibitors together, which can work better for some cancers but causes more side effects. [2]

Side effects

Because checkpoint inhibitors make the immune system more active, it can attack healthy organs. These are called immune-related adverse events. They can affect almost any part of the body. [3] [4]

Common side effects

• Tiredness.
• Skin rash or itching.
• Diarrhea or belly pain, which can be a sign of colitis (inflammation of the colon).
• Thyroid problems, which can cause tiredness, weight change, or feeling too hot or cold.
• Joint pain.

Less common but serious

• Pneumonitis: inflammation of the lungs, with cough or shortness of breath.
• Hepatitis: inflammation of the liver.
• Problems with the pituitary or adrenal glands, which can cause headache, weakness, or low blood pressure.
• Type 1 diabetes, which can cause extreme thirst and frequent urination.
• Myocarditis: inflammation of the heart. This is rare but can be serious.
• Nerve or muscle problems.

Timing

Most side effects start in the first few months. But they can start at any time, even months after the last dose. [3] [4] Tell any doctor who treats you that you have had immunotherapy.

CAR T-cell side effects

CAR T-cell therapy has its own risks. These include cytokine release syndrome, which causes fever, low blood pressure, and trouble breathing. It can also cause nerve problems such as confusion or trouble speaking. People are usually watched closely in or near the treatment center for the first weeks. [1]

What your doctor looks at

The American Society of Clinical Oncology guideline describes how teams watch for and manage these side effects. [4]

• Before treatment: blood tests for liver, kidney, thyroid, and blood sugar, and a review of autoimmune diseases you may have.
• During treatment: regular blood tests and questions about new symptoms.
• Grading: each side effect gets a grade from 1 (mild) to 4 (life threatening).
• Mild side effects: treatment often continues, with close watch.
• Moderate or severe side effects: treatment is often paused, and steroids or other drugs that calm the immune system are given.
• Hormone problems, such as low thyroid, often need hormone replacement, sometimes for life.

Most side effects get better with treatment, especially when found early. [4]

Who may need extra care

Tell your team if you have an autoimmune disease, such as rheumatoid arthritis, lupus, or inflammatory bowel disease, or if you have had an organ transplant. Immunotherapy can make these conditions worse. It may still be an option, but it needs careful planning. [5]

Questions to ask your clinician

• What type of immunotherapy will I get, and how often?
• What are the most likely side effects for this drug?
• Which symptoms should I report right away, and who do I call after hours?
• What blood tests will I need during treatment?
• How will we know if the treatment is working?
• Is it safe with my other health conditions and medications?
• Should I carry a wallet card that says I am on immunotherapy?

When to get care quickly

Call your oncology team right away, or go to the emergency department, if you have:

• Trouble breathing, chest pain, or a new or worse cough.
• Severe diarrhea, blood in your stool, or severe belly pain.
• Yellow skin or eyes, or very dark urine.
• A severe headache, confusion, or vision changes.
• Fainting, extreme weakness, or very low blood pressure.
• Extreme thirst and frequent urination.
• A fever, especially after CAR T-cell therapy.

Call 911 for severe trouble breathing, chest pain, or fainting. Tell the emergency team that you are on immunotherapy.

Bottom line

Immunotherapy helps your immune system attack cancer. It has changed care for many cancers. Its side effects come from an overactive immune system, and they can affect almost any organ, at any time. Most can be treated well if you report them early. Learn the warning signs and keep your team's phone number close.

Primary AI can show you the guideline and study sources behind this topic in plain language, so you can bring better questions to your appointment.