Immune-Related Side Effects

NCI offers a shortcut for reading these side effects: look for the suffix "-itis," which means inflammation. Colitis is inflammation of the colon. Pneumonitis is inflammation of lung tissue. Hepatitis is the liver. Nephritis is the kidney. Myocarditis is the heart muscle. Thyroiditis, hypophysitis, myositis, uveitis. Same pattern every time.

Checkpoint inhibitors do not attack organs directly. They release a brake on your immune system. The freed immune cells then sometimes attack healthy tissue along with cancer. The result is autoimmune inflammation. That is why the treatment is usually steroids, not antibiotics.

Chemotherapy side effects are predictable. Counts fall around day 7 to 14, then recover, then it repeats.

Immune-related side effects have no cycle. NCI states that they can occur at any point during and after treatment, and that doctors and nurses cannot know in advance when or whether they will happen or how severe they will be.

That has a practical consequence people often miss. Finishing treatment does not close the window. A rash, a cough, or unexplained fatigue three months after your last infusion still needs reporting as a possible immune effect.

The pembrolizumab label reports rates across 2,799 patients, which gives a useful sense of scale.

Hypothyroidism was the most common at 8%, and most of those people needed long-term thyroid hormone replacement. Hyperthyroidism and pneumonitis were each 3.4%. Colitis was 1.7%. Adrenal insufficiency was 0.8%, hepatitis 0.7%, hypophysitis 0.6%, nephritis 0.3%, and type 1 diabetes 0.2%.

Two details in that data matter more than the headline percentages. Pneumonitis was fatal in 0.1% of patients, and 67% of those who developed it needed systemic steroids. And every single person who developed type 1 diabetes required insulin permanently.

Rates rise in specific settings. In people with classical Hodgkin lymphoma treated with pembrolizumab alone, pneumonitis occurred in 8%. In people receiving it after lung cancer surgery, 7%. The label notes that prior chest radiation raises pneumonitis risk.

NCI groups these by how common they are.

These are the more common ones.

• Gut. Colitis brings belly pain, diarrhea, and black or bloody stools. Mild hepatitis is often found only on a blood test.
• Pituitary. This is the most common endocrine problem. It causes headaches and fatigue.
• Adrenal glands. Fatigue, muscle weakness, loss of appetite, weight loss, and belly pain.
• Thyroid. An underactive gland brings weakness, constipation, dry skin, weight gain, and feeling cold. An overactive one brings diarrhea, weight loss, sweating, and heat sensitivity. Atrial fibrillation is rare.
• Pancreas. Severe belly pain, nausea, and vomiting.
• Muscles and joints. Pain and weakness. Muscle inflammation is called myositis.
• Lungs. Pneumonitis brings breathlessness and a bad cough.
• Skin. Rashes, itching, blisters, and sores.

These are less common.

• Blood. Easier bleeding and bruising from low platelets. Anemia and neutropenia also occur.
• Eyes. Vision changes or eye pain from uveitis or episcleritis.
• Heart. Myocarditis can lower blood pressure. It can rarely upset the heartbeat or weaken pumping.
• Kidney. Nephritis can cut urine output or cause blood in the urine.
• Liver. Hepatitis turns the skin and eyes yellow. It also brings dark urine, nausea, belly pain, and bruising.
• Nervous system. Tingling, numbness or weakness in the hands, feet and sometimes the face. NCI says inflammation of the brain, called encephalitis, may start as mild flu-like symptoms or go straight to sudden high fever, confusion, hallucinations, seizures and vomiting.

The hormone group is the trap. Fatigue, feeling cold, and constipation are easy to blame on the cancer itself. NCI notes that hormone levels are checked often for that reason. These problems show up on blood tests before you notice them. Thyroid changes during immunotherapy covers what those results look like.

Drug labels define when treatment is held or abandoned, and the liver rules are the most concrete.

Where the liver is not involved by tumour, pembrolizumab is withheld when AST or ALT, two liver enzymes, rise above 3 times the upper limit of normal, or when total bilirubin rises above 1.5 times normal. It is stopped permanently when AST or ALT exceed 8 times normal, or bilirubin exceeds 3 times normal. The label sets different, higher numbers when the tumour does involve the liver.

For colitis, grade 2 or 3 means the drug is withheld. For pneumonitis, grade 3 or 4 means permanent discontinuation. Grade 2 or 3 rising creatinine with nephritis means the drug is withheld.

Being held is not the same as being finished. In the pembrolizumab data, everyone whose drug was withheld for pneumonitis or colitis restarted after symptoms improved, and 23% then had a recurrence of the same problem.

If you already have lupus, rheumatoid arthritis, inflammatory bowel disease, or a transplant, this conversation happens before the first dose, not after.

NCI states that people with an autoimmune disease should discuss it with their provider before starting treatment. The major trials excluded people whose autoimmune disease had needed systemic treatment within the previous two years, and anyone taking immunosuppressive medicine, so the evidence base largely does not cover this group. Keytruda and chemotherapy sets out those trial entry rules.

That does not automatically rule treatment out. It means the risk conversation is individual and should involve whoever manages your autoimmune condition.

Carry a card or note stating that you receive immune checkpoint inhibitor therapy, with the drug name and the date of your last dose.

This matters in an emergency room. Diarrhea here is handled differently from an ordinary stomach bug. Breathlessness is worked up differently too. A clinician who does not know you are on one of these drugs may reach for the wrong treatment. Delay in starting steroids is what turns treatable swelling into organ damage.

Immunotherapy pneumonitis and new breathing problems covers the lung symptom in more detail, since it is the one with the highest fatality rate on the label.

Do not wait for a call-back for severe breathlessness, chest pain, fainting, a seizure, sudden confusion or hallucinations, swelling of the face or throat, or a sudden high fever. Tell whoever sees you that you are on an immune checkpoint inhibitor, and name the drug.

• A new cough, breathlessness, or chest tightness, even mild. Do not wait to see if it settles.
• 4 or more loose stools a day above your usual number, or any blood, mucus, or black color in stool.
• Yellowing of the eyes or skin, or urine turning dark.
• Sudden intense thirst, urinating far more than usual, and losing weight. This can be type 1 diabetes appearing.
• A headache that is new and persistent, especially with fatigue or dizziness on standing.
• Chest pain, palpitations, or breathlessness lying flat.
• Eye pain or blurred vision.
• A rash that spreads fast, blisters, or involves the mouth, eyes, or genitals.
• Your temperature reaches 100.4 degrees F (38 C). MedlinePlus, reviewed October 2024, uses 100.4 F; NCI's infection page, reviewed January 2020, uses 100.5 F. Use the lower, newer number.

When you call, say which drug you are on and when your last dose was. That single sentence changes the triage.

Immunotherapy covers how these drugs work and which cancers they are used in.

• https://www.cancer.gov/about-cancer/treatment/side-effects/organ-inflammation
• https://www.cancer.gov/about-cancer/treatment/types/immunotherapy/side-effects
• https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9333c79b-d487-4538-a9f0-71b91a02b287
• https://www.cancer.gov/about-cancer/treatment/side-effects/infection
• https://medlineplus.gov/ency/patientinstructions/000913.htm