Side Effects of Immunotherapy

Immunotherapy is a cancer treatment that helps the immune system recognise and attack cancer cells. Some immunotherapies may produce long-lasting effects by enhancing the immune response against cancer. 

As with other cancer treatments, immunotherapy medications may cause side effects. Some are mild. Others can be more severe, affecting healthy tissues and organs in your body or causing widespread inflammation.

Keep reading to learn more about the most common immunotherapy side effects, why and when they occur, and how to manage them.

Immunotherapies work by revving up your immune system so it can attack cancer cells more effectively. Sometimes, though, an overactive immune system mistakenly attacks healthy cells, tissues, and organs too. Doctors call this damage immune-related side effects, or immune-related adverse events (irAEs).

Immunotherapy can cause immune-related side effects for several reasons, including (1,2,3):

• Some immunotherapy drugs switch off the immune system’s safety brakes, allowing T cells to attack tumours more aggressively, but with less accuracy.  
• Cancer cells can look like healthy cells, and activated immune cells sometimes attack the wrong target.
• As they work, immune cells release chemical signals called cytokines, which can cause flu-like symptoms throughout the body.

Side effects can start within days after starting immunotherapy, though most appear several weeks to months into treatment. Because immunotherapy keeps your immune system active, it’s also possible for side effects to develop months after treatment ends. 

Immunotherapy side effects can affect any part of your body. What side effects you might experience, and when, can vary widely depending on: 

• Which drugs you’re taking.
• How long treatment lasts.
• Whether you’re also having other treatments, like chemotherapy.
• Your cancer type and stage.
• Your overall health.

Your cancer specialist can tell you what you might expect, but in general side effects might include (1):

• In the first few weeks - Fatigue, skin rashes, or flu-like symptoms like fever, chills, or muscle aches.
• After a month - Joint pain, nausea, stomach pain, diarrhoea or other digestive changes.
• Months to a year later - Chronic inflammation in your lungs, liver, or nerves, as well as thyroid or hormonal problems. 

Because immunotherapy is a relatively new type of cancer treatment, doctors are still studying the long-term side effects. Known ones include:

• Hormone problems such as an underactive thyroid or inadequate adrenal hormones.
• Arthritis or nerve pain.
• Liver inflammation or hepatitis.
• Colon inflammation (colitis), which can cause long-term diarrhoea.

These long-term side effects may gradually improve over time.

Side effects can vary depending on the type of immunotherapy treatment you receive (1).

• Checkpoint inhibitors often cause mild or moderate effects, like skin rashes or diarrhoea. Monoclonal antibodies can cause flu-like symptoms, bleeding problems, skin rashes, and slower wound healing.
• CAR T-cell therapy can trigger infections or cytokine release syndrome, an immune reaction that causes fever, low blood pressure, and difficulty breathing. It’s also possible to experience neurological symptoms, such as confusion or difficulty speaking, with this treatment.
• Cancer vaccines typically cause mild, local reactions, like pain, redness, or swelling at the injection site, or mild flu-like symptoms.

Your risk of severe side effects increases if you receive more than one treatment. Ask your doctor what you might expect from your treatment plan.

Side effects can be frightening, but they’re often manageable. Your doctor might prescribe steroids to reduce inflammation or other medications to ease nausea, diarrhoea, or pain. 

You can also help manage side effects at home by:

• Prioritising rest and sleep.
• Getting regular moderate exercise.
• Aiming to eat regularly and including protein-rich foods to help maintain strength and muscle mass. If eating becomes difficult, speak with your healthcare team or a dietitian, who may recommend practical dietary strategies or oral nutritional supplements.
• Staying hydrated.
• Protecting your skin with moisturisers and sunscreen.

Immunotherapy and chemotherapy kill cancer in different ways, so their side effects differ too. Immunotherapy treatments are less toxic to healthy cells, so they may be easier to tolerate, but this varies from person to person.

Tell your medical team about any and all side effects, especially if they are new or worsening, or affect your daily life. Catching side effects early makes them easier to manage. 

Regular follow-up during and after treatment is important too, because certain side effects may appear weeks or months after your treatment ends. 

Call your provider and go to the emergency department if you have:

• Difficulty breathing
• Chest pain
• Severe abdominal pain
• Watery diarrhoea or more than six bowel movements per day
• A high fever
• Seizures

These can be warning signs of immunotherapy toxicity, and your doctor may need to pause or stop treatments.

Immunotherapy is a promising treatment for many cancer types, but it can come with side effects, and they can vary widely among people. Stay in close contact with your healthcare team so they can monitor and treat any side effects early and adjust treatments as needed.