What Are the Side Effects of Immunotherapy for Lung Cancer?

Not everybody gets side effects from immunotherapy - but if they do happen, the timing of symptom onset is less predictable than with chemotherapy.

Rather than directly damaging rapidly dividing cells, commonly used immunotherapies, known as checkpoint inhibitors, alter how the immune system responds to cancer. Sometimes that immune response also affects healthy tissues, causing inflammation in different parts of the body.

Many side effects can be managed successfully, particularly when recognised early. Knowing which changes to report is therefore an important part of treatment.

Why Does Immunotherapy Cause Side Effects?

Checkpoint inhibitors work by blocking signals that normally help regulate immune activity. This can allow immune cells to mount a more effective response against cancer, but it can also cause inflammation in healthy organs.

These problems are often called immune-related adverse effects.

Understanding these risks is an important part of developing a personalised immunotherapy treatment plan. The potential benefits of treatment need to be considered alongside the possible side effects, the patient's general health and the characteristics of their cancer.

Immune-related side effects behave differently from many conventional chemotherapy side effects. They can affect almost any organ and may occasionally appear after treatment has been paused or completed.

This does not mean everyone receiving immunotherapy will develop serious problems. The type, timing, and severity of side effects vary considerably between patients and depending on the immunotherapy being used.

Fatigue Can Be Difficult to Interpret

Tiredness is commonly reported during cancer treatment, but fatigue has several possible causes.

It may relate to the cancer itself, treatment, sleep, nutrition, anaemia or another medical problem. With immunotherapy, significant or changing fatigue can sometimes also be associated with inflammation affecting hormone-producing glands.

For that reason, new or unusually severe tiredness should not automatically be dismissed as an unavoidable part of treatment.

When medically appropriate, staying physically active can help some patients manage cancer-related fatigue and maintain strength. An individualised approach to exercise during lung cancer treatment is particularly important if breathlessness, reduced fitness or treatment side effects limit activity.

Skin Changes Are Among the More Visible Effects

Immunotherapy can cause changes to the skin, including:

• Rash
• Itching
• Dry skin
• Changes in skin colour

Many reactions are mild and can be treated without permanently stopping cancer therapy. More extensive, painful, blistering or rapidly worsening skin changes need prompt medical assessment.

It is important not to assume that every rash is caused by immunotherapy. Other medicines, infections, and unrelated skin conditions can produce similar symptoms, so doctors may need to assess the cause before recommending treatment.

Diarrhoea Can Be More Than an Upset Stomach

Diarrhoea during immunotherapy deserves attention because checkpoint inhibitors can cause inflammation of the bowel, known as colitis.

Mild changes in bowel habits may initially seem unimportant. However, frequent diarrhoea, abdominal pain, blood or mucus in the stool, fever, or difficulty maintaining fluids should be reported promptly.

The distinction matters because immune-related colitis can worsen without appropriate treatment.

Patients should therefore tell their oncology team about a clear change from their normal bowel pattern rather than waiting until symptoms become severe.

A New Cough or Breathlessness Needs Particular Attention

For someone being treated for lung cancer, respiratory symptoms can be especially difficult to interpret.

The cancer itself may cause cough or breathlessness. Infection, a blood clot, previous radiotherapy and underlying lung conditions can also produce similar symptoms.

Immunotherapy introduces another possible cause: pneumonitis, an inflammatory reaction affecting the lungs.

Symptoms can include a new or worsening cough, increasing breathlessness, chest discomfort or reduced ability to carry out normal activities. Pneumonitis is less common than some milder immunotherapy effects, but it can become serious and requires appropriate assessment.

This is one reason a change in respiratory symptoms during immunotherapy should not simply be assumed to be part of lung cancer.

The wider role of immunotherapy in lung cancer treatment includes careful monitoring for these immune-related effects as well as assessing whether the cancer is responding.

The Liver Can Become Inflamed Without Obvious Symptoms

Immune-related inflammation of the liver is known as hepatitis.

Unlike a skin rash or diarrhoea, liver inflammation may initially cause few noticeable symptoms. It can sometimes first be identified through abnormalities in routine blood tests.

When symptoms do occur, they may include nausea, reduced appetite, abdominal discomfort, dark urine or yellowing of the skin or eyes.

Regular blood monitoring during immunotherapy is therefore important even when someone feels relatively well.

Immunotherapy Can Affect Hormone-Producing Glands

Checkpoint inhibitors can sometimes affect endocrine glands, including the thyroid, pituitary and adrenal glands.

The resulting symptoms may initially appear quite general. Fatigue, headaches, dizziness, weakness, weight changes, altered mood, or feeling unusually cold can have many possible explanations.

Blood tests can help identify changes in hormone levels. Some endocrine effects may require long-term hormone replacement even after the immune inflammation itself has been controlled.

This is another reason symptoms should be considered in context rather than attributed automatically to cancer or general treatment fatigue.

Less Common Side Effects Can Affect Other Organs

Because the immune system operates throughout the body, immune-related adverse effects are not limited to the lungs, bowel, skin and endocrine glands.

Less commonly, inflammation may affect the kidneys, nervous system, muscles, joints, heart, eyes or other organs.

Patients do not need to memorise every possible complication. What matters more is reporting symptoms that are new, persistent, worsening or unusual for them.

This is particularly important when several treatments are being given together. For example, chemoimmunotherapy for lung cancer can produce side effects from both components, so establishing the likely cause can influence how the problem is managed.

How Are Immune-Related Side Effects Treated?

Management depends on which organ is affected and how severe the reaction is.

Mild effects may only require symptom management and close monitoring. More significant immune-related reactions may require immunotherapy to be temporarily withheld. Corticosteroids are commonly used for many clinically significant inflammatory reactions, while some complications require different or additional treatment.

Serious reactions are rare, but can require hospital assessment and, in some cases, further immune-suppressing treatment.

The aim is to control the inflammatory reaction while considering whether immunotherapy can safely be restarted later. That decision is individual and depends on the type and severity of the side effect, how well it resolves and the expected benefit of continuing treatment.

Early reporting is important because immune-related problems can sometimes progress quickly, and prompt assessment allows appropriate treatment to begin sooner.

Side Effects Can Occasionally Appear After Treatment Stops

One unusual feature of checkpoint inhibitor immunotherapy is that immune-related side effects are not restricted to the period when treatment is actively being given.

Some can first develop weeks or months after the final treatment. Delayed reactions are less common, but previous immunotherapy remains important information when a new health problem is being assessed.

This can be particularly relevant for people with stage 4 lung cancer, where treatment may change over time depending on how the cancer responds and which options remain appropriate.

Even if immunotherapy has been stopped and another treatment has begun, a new symptom may still need to be considered in the context of previous immunotherapy.

Patients should therefore continue to mention their previous immunotherapy when seeking medical attention for new symptoms, even if they are no longer receiving the drug.

This is particularly useful if assessment takes place outside the oncology team, because it alerts other healthcare professionals to immune-related complications as a possible explanation.

Monitoring Is Part of Immunotherapy Treatment

Regular review is not only about checking whether the cancer is responding.

Blood tests can monitor liver, kidney and thyroid function, while consultations provide an opportunity to discuss changes in breathing, bowel habits, skin, energy levels and other symptoms.

Scans may also be required as part of monitoring the lung cancer itself.

If symptoms are becoming difficult to interpret, or you have questions about whether the balance between treatment benefit and toxicity remains appropriate, a second opinion can provide an independent review of the diagnosis, response to treatment, and available options.

When Should You Contact Your Oncology Team?

Patients are usually given specific instructions about which symptoms to report and who to contact during treatment. Those instructions should always take priority because recommendations can vary according to the drug and individual circumstances.

In general, report promptly any new or worsening breathlessness, persistent diarrhoea, significant abdominal pain, severe or rapidly spreading rash, yellowing of the skin or eyes, marked weakness, confusion, or other substantial changes.

You do not need to decide for yourself whether a symptom is definitely caused by immunotherapy before contacting the team. If you need additional specialist guidance about treatment-related symptoms or how they may affect ongoing treatment decisions, a private oncology consultant can help review them in the context of your diagnosis and treatment plan.

The important point is that immune-related effects are often easier to manage when they are recognised early.

About Dr James Wilson

Immunotherapy has created important treatment opportunities for people with lung cancer, but careful monitoring remains an essential part of using these treatments safely.

Dr James Wilson is a consultant clinical oncologist in full-time private practice in Central London, specialising in lung cancer and advanced radiotherapy. His practice includes systemic cancer treatments such as immunotherapy, with an emphasis on clear explanations, individualised treatment decisions and careful management throughout the treatment pathway.