Immunotherapy Pneumonitis: What to Ask

Pneumonitis means inflammation of lung tissue. When it follows an immune checkpoint inhibitor, the FDA labels call it immune-mediated pneumonitis. Nivolumab's label gives the working definition used in trials. It is pneumonitis that required steroids, with no clear alternative cause found.

The frequency is documented, not guessed. The pembrolizumab safety database covers 2,799 patients. Immune-mediated pneumonitis occurred in 3.4% of them, which is 94 people. By severity, that was 1.3% Grade 2, 0.9% Grade 3, 0.3% Grade 4, and 0.1% fatal. Nivolumab used alone gave a nearly identical picture. It affected 3.1% of 1,994 patients, with 2.1% Grade 2, 0.9% Grade 3, and under 0.1% Grade 4.

Both labels flag the same risk factor. Pneumonitis is more common in people who have had radiation to the chest before.

This is the part worth asking about by name, because the range is wide.

• Pembrolizumab alone, across all cancers: 3.4%.
• Pembrolizumab alone in classical Hodgkin lymphoma (389 patients): 8%, with Grade 3–4 in 2.3%. In this group, rates were similar with and without prior chest radiation.
• Pembrolizumab alone as adjuvant treatment after resected non-small cell lung cancer in KEYNOTE-091 (580 patients): 7%, including 1% Grade 3, 0.3% Grade 4, and 0.2% fatal.
• Nivolumab every 2 weeks with ipilimumab every 6 weeks in non-small cell lung cancer (576 patients): 9%, including 4% Grade 2, 3.5% Grade 3, and 0.5% Grade 4. Four patients, 0.7%, died of pneumonitis.

So the same side effect ranges from roughly 3% to roughly 9%. What moves it is the drug, the cancer, and whether a second checkpoint inhibitor is in the mix. A number quoted from a general immunotherapy leaflet may not be the number for a specific plan.

The response follows a severity grade. That grade comes from the Common Terminology Criteria for Adverse Events. Pembrolizumab's dosage-modification table is explicit.

• Grade 2 pneumonitis: withhold the drug. It may be resumed after a corticosteroid taper, for people back at Grade 0 or 1. Discontinue permanently if there is no complete or partial resolution within 12 weeks of starting steroids. Also discontinue if prednisone cannot be cut to 10 mg a day or less within those 12 weeks.
• Grade 3 or Grade 4 pneumonitis: permanently discontinue.

Steroid dosing has its own instruction, covering any immune-mediated reaction that forces a hold or a stop. The dose is a weight-based daily amount of prednisone, or an equivalent steroid, set by the team. It runs until improvement to Grade 1 or less. Then the taper begins, continuing over at least 1 month. If corticosteroids do not control the reaction, other systemic immunosuppressants are considered.

Outcomes after a hold are documented too. Systemic corticosteroids were required in 67% of the pembrolizumab pneumonitis cases. With nivolumab used alone, that figure was 100%. Pneumonitis resolved in 59% of the pembrolizumab cases and 84% of the nivolumab cases. Among people whose drug was held and later restarted, about 23% had pneumonitis return with pembrolizumab. With nivolumab it was 29%.

The label instruction for any suspected immune-mediated reaction is to start a workup that excludes other causes, including infection. That is not caution for its own sake. The treatments diverge sharply. High-dose corticosteroids for pneumonitis. Antimicrobials for pneumonia. Blood thinners for a clot in the lung. Guessing wrong in either direction costs time.

The overlap list is long. Cough and breathlessness during checkpoint inhibitor therapy have many possible sources. Bacterial or viral pneumonia. Cancer growing in the lungs or the lining around them. A clot in the lung. Radiation pneumonitis after chest radiotherapy. Fluid overload or heart failure. Or long-standing lung disease. Anemia can also cause breathlessness with no lung problem at all.

Timing is a weak clue rather than a decisive one. Immune-mediated reactions usually appear during treatment. But the labels state plainly that they can also appear after a checkpoint inhibitor has been stopped. A cough three months after the last infusion is not automatically unrelated.

Neither label sets a home threshold. There is no pulse-oximeter reading, no temperature, no breathing rate. Severity is graded in the clinic, on symptoms, function, and oxygen need. So the useful number is whatever the oncology team puts in an individual urgent-call plan. Getting that number written down before it is needed is the most practical step here.

A pulse oximeter is the small clip-like device that goes on a finger. As MedlinePlus describes it, it reports the percentage of red blood cells that are full of oxygen.

Reasons to make contact the same day, rather than waiting for the next visit: a new cough; new or worsening breathlessness; breathlessness at rest or when lying flat, rather than only with activity; chest discomfort; or a fever alongside any of these. For anyone asked to check oxygen readings at home, a drop from the usual baseline counts as new information, even without a specific cutoff in mind.

Fever deserves its own note, because federal sources differ slightly. NCI's infection page defines fever as 100.5 °F (38 °C) or higher. MedlinePlus, on a page carrying a review date of October 2024, uses 100.4 °F (38 °C) or higher. The MedlinePlus figure is the more recently dated of the two, and the lower one. Either way, fever plus breathing symptoms during checkpoint inhibitor treatment is a call rather than a wait. It raises the possibility of infection, which changes the treatment entirely.

Having these ready shortens the conversation considerably:

• The exact drug name, and whether it is given alone or with a second checkpoint inhibitor such as ipilimumab.
• The date of the most recent infusion, and how many cycles have been given.
• Whether chest radiation has ever been given, and when.
• When the symptom started, whether it is getting worse, and what makes it worse.
• Any fever, colored sputum, or sick contacts, which push toward infection.
• Current steroid use, since that changes both the picture and the plan.
• Home oxygen readings, if the team requested them.

What percentage risk of pneumonitis applies to this exact regimen, rather than to immunotherapy in general? Would earlier chest radiation change that estimate? At what grade would this drug be held, and at what grade stopped for good? If steroids are started, at what dose, and how long is the taper expected to run? Recurrence after restarting runs about one in four, so what is the plan for restarting? And what workup happens first to rule out infection and clot?

Related reading: immune-related side effects covers the wider pattern these reactions follow, immunotherapy colitis covers the gut version of the same problem, and what immunotherapy is explains how checkpoint blockade works in the first place.

The team's own urgent-call plan comes first. Where no plan has been written down yet, this is the shape of it.

• Call 911 or go to an emergency department if you have severe difficulty breathing, meaning you are gasping or cannot get a sentence out, or breathlessness that comes on suddenly. Do the same for chest pain or pain in the upper back, a heart that is racing, coughing up blood, or if someone passes out. The NHS puts all of those in the emergency group, because a clot in the lung looks much like pneumonitis and is treated in a different way entirely. Do not drive yourself.
• Call your care team the same day if you have a new cough, breathlessness that is new or getting worse, breathlessness at rest or when lying flat rather than only on exertion, or chest discomfort. Call the same day for a temperature of 100.4°F (38°C) or higher alongside any of those, since fever raises the possibility of infection and changes the plan. If the team asked you to check oxygen readings at home, a drop from your usual baseline is worth the call even without a set cutoff.
• Unless chemotherapy is running too. In that case 100.4°F (38°C) stops being a same-day matter: CDC counts a fever during chemotherapy as a medical emergency. Call the team the moment you see the reading, at any hour, and go to an emergency department if nobody answers.
• Call your care team within a day or two if a mild cough or slight breathlessness has been creeping up over days but is not yet limiting you. Say when it began and whether it is worse. Mention the drug by name, the date of the last infusion, and any earlier chest radiation, and do this even if the last dose was months ago. Both labels say these reactions can begin after a checkpoint inhibitor has been stopped.

This page is a planning aid. It cannot diagnose the cause of a symptom or replace the instructions from an oncology team.

• DailyMed — KEYTRUDA (pembrolizumab) full prescribing information
• DailyMed — OPDIVO (nivolumab) full prescribing information
• MedlinePlus — Blood Oxygen Level
• MedlinePlus — Cancer treatment, preventing infection
• NCI — Infection and Neutropenia during Cancer Treatment
• NHS — Pulmonary embolism