Immunotherapy has changed the way many cancers are treated by helping the immune system recognise and attack cancer cells. But because these treatments influence the immune system, they can sometimes affect healthy tissues as well.
This can lead to side effects that are different from those commonly associated with chemotherapy or radiation therapy. Not everyone receiving immunotherapy develops side effects, and the type and severity can vary considerably from one person to another.
If you are learning about cancer immunotherapy, understanding its possible side effects can help you recognise changes early and know when to contact your healthcare team.
Why Can Immunotherapy Cause Side Effects?
Some immunotherapy drugs work by removing the signals that normally keep the immune system under control. This can help immune cells attack cancer, but in some people the immune response may also affect healthy organs and tissues.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
These problems are often called immune-related adverse events (irAEs). They can affect different parts of the body, including the skin, digestive system, lungs, liver, kidneys, thyroid and other hormone-producing glands, heart, and nervous system.
The risk depends on several factors, including the type and dose of immunotherapy, the type and stage of cancer, and a person's overall health. Doctors cannot always predict whether a patient will develop a side effect or how severe it will be.
Common Immunotherapy Side Effects
Many immunotherapy side effects are mild and can be managed with appropriate monitoring and treatment. Some of the more commonly reported problems include:
- Fatigue: Feeling unusually tired or lacking energy.
- Skin changes: Rash, itching, dryness or other skin irritation.
- Diarrhoea: This may occur when the digestive tract becomes affected.
- Nausea: Some people experience nausea or changes in appetite.
- Muscle or joint aches: These can occur during treatment.
- Fever or flu-like symptoms: Chills, headache, weakness or body aches may occur with some forms of immunotherapy.
These symptoms can also occur for reasons unrelated to immunotherapy, including the cancer itself or other treatments. That is why new or worsening symptoms should be discussed with the healthcare team rather than automatically attributed to treatment.
Immune-Related Side Effects: What Patients Should Watch For
One of the important differences between immunotherapy and many other cancer treatments is that immune-related side effects can involve almost any organ. They may appear during treatment, and some can occur after treatment has ended.
Skin
Skin-related problems are among the more common immune-related effects. You may notice a rash, itching, redness or changes in the skin.
Although many skin reactions are manageable, rapidly worsening rashes, extensive skin peeling, blistering, or sores should be reported promptly.
Digestive System
Inflammation of the intestines, known as colitis, can cause diarrhoea, abdominal pain or cramping. Blood or black stools can be a sign of more significant inflammation and require prompt medical attention. It is useful to keep track of changes in bowel habits during treatment rather than waiting for symptoms to become severe.
Lungs
Immunotherapy can occasionally cause inflammation of the lungs, known as pneumonitis. Symptoms may include a new or worsening cough, shortness of breath or chest discomfort.
Breathing problems should not be ignored, particularly in someone who is already being treated for lung cancer or another condition affecting the lungs.
Liver
Inflammation of the liver, called hepatitis, may not always cause noticeable symptoms in the early stages. This is one reason why blood tests are often used to monitor liver function during treatment.
Possible symptoms can include unusual fatigue, nausea, abdominal discomfort, dark urine, yellowing of the skin or eyes, or unusual bruising or bleeding.
Thyroid and Other Hormone-Producing Glands
Immunotherapy can affect the thyroid and other endocrine organs. This may lead to an underactive or overactive thyroid or other hormonal changes.
Symptoms can be subtle. Changes in energy levels, weight, temperature tolerance, heart rate or mood may sometimes be related to hormonal problems. Blood tests can help identify these changes.
Kidneys
Inflammation of the kidneys, known as nephritis, is less common but can affect kidney function. Blood and urine tests may help detect kidney problems during treatment.
Heart
Inflammation of the heart muscle, called myocarditis, is uncommon but potentially serious. New chest pain, shortness of breath, an irregular heartbeat or unexplained severe weakness should be assessed urgently.
Nervous System
Rarely, immunotherapy can affect the nervous system. Symptoms may include unusual weakness, numbness, tingling, changes in sensation, difficulty walking, confusion or problems with muscle control. Because some neurological side effects can progress quickly, new neurological symptoms should be reported without delay.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Can Immunotherapy Side Effects Happen After Treatment?
Yes. Although many side effects occur during treatment, immune-related problems can sometimes develop after immunotherapy has been completed.
This is important because a new symptom should not automatically be dismissed simply because your last immunotherapy dose was weeks or months ago.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Tell your doctor about your previous immunotherapy treatment so that it can be considered when the cause of a new symptom is assessed.
Some immune-related effects can also persist for an extended period after treatment. The timing varies according to the type of side effect and the individual patient.
How Are Immunotherapy Side Effects Managed?
Management depends on the affected organ, severity of symptoms and the specific immunotherapy being used. For mild problems, the healthcare team may recommend monitoring, supportive treatment or medicines to relieve symptoms.
If a significant immune-related reaction is suspected, immunotherapy may need to be paused while the problem is evaluated. More serious immune-related inflammation may require medicines that suppress the overactive immune response, including corticosteroids in appropriate situations.
Other treatments may be considered when side effects do not respond adequately to initial management. The important point is that treatment should be guided by the medical team. Patients should not stop, restart or change their immunotherapy medicines on their own.
What Monitoring Is Done During Immunotherapy?
Regular monitoring helps doctors identify certain problems before they become severe. Depending on the immunotherapy and the cancer being treated, monitoring may include:
- Reviewing new symptoms at each visit
- Blood tests to assess liver and kidney function
- Thyroid and other hormone tests when appropriate
- Assessment of breathing symptoms
- Physical examinations and other tests based on symptoms
Not every possible immune-related side effect can be detected through routine blood tests. Paying attention to how you feel and communicating changes to your healthcare team remains an important part of monitoring.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
The Bottom Line
Immunotherapy side effects can range from mild problems such as fatigue, rash and diarrhoea to less common but potentially serious inflammation affecting organs such as the lungs, liver, heart, kidneys or nervous system. They do not occur in everyone, and their timing and severity can vary.
The most important thing is to recognise new or worsening symptoms early and communicate them to your healthcare team. Some immune-related side effects can be managed effectively when identified promptly, while serious symptoms may require urgent assessment and treatment.
Understanding what to watch for does not mean expecting complications. It simply gives you a clearer idea of what changes deserve attention while you are receiving immunotherapy.
