Immunotherapy Pneumonitis Misdiagnosed as COPD or a Cold?

A person on immunotherapy mentions a new cough, or says the stairs have suddenly gotten harder. Everyone reaches for the obvious explanation: it’s the cancer, a lingering cold, or the COPD flaring again.

Sometimes that’s right. Sometimes it’s exactly how a treatable, treatment-caused lung condition goes unrecognized until it becomes an emergency.

That condition is checkpoint inhibitor pneumonitis, lung inflammation caused by the immunotherapy itself. We cover what it is, how often it happens, and how it differs from radiation pneumonitis in our article on pneumonitis after radiation and immunotherapy.

This article focuses on one problem: why it gets mistaken for something else, what guidelines require once it’s suspected, and when a delay becomes a legal issue under New York law.

Why It Matters When Immunotherapy Pneumonitis Is Missed

Most cases of immunotherapy pneumonitis are mild or moderate and respond to prompt steroid treatment. But the severe cases move fast. A 2018 Vanderbilt-led analysis in JAMA Oncology found that pneumonitis caused 35% of fatal toxicities from PD-1 and PD-L1 drugs, the class that includes pembrolizumab (Keytruda) and nivolumab (Opdivo). In a review of patients at seven academic centers, the median time from the first symptom to death was 32 days.

That timeline is why a week spent blaming breathlessness on COPD, or a few days of waiting out a “cold,” can matter so much.

Why Pneumonitis Gets Mistaken for Something Else

The early symptoms are a dry cough, shortness of breath, fatigue, low-grade fever, and chest discomfort. Those are the same symptoms produced by many conditions lung cancer patients already have:

• A COPD flare, which causes breathlessness and cough

• Cancer progression in the lungs

• A respiratory infection, including pneumonia, flu, or COVID-19

• Radiation pneumonitis from earlier chest radiation

• Heart failure, fluid around the lung, or a blood clot

For a patient with lung cancer, nearly every one of these is plausible, which is why pneumonitis can hide in plain sight.

Our page on lung cancer signs and symptoms shows how much those symptoms overlap. The error also runs in reverse, a pattern we cover in our article on lung cancer misdiagnosed as pneumonia.

Timing misleads people too. Pneumonitis often appears in the first few months of treatment, but it can appear within days, after a year or more, or even after immunotherapy has stopped. A patient who has done well for many months may not be treated as someone at risk, by the care team or by themselves.

And pneumonitis is partly a diagnosis of exclusion. Clinicians have to rule out infection, tumor growth, heart problems, and clots. That workup is appropriate. The danger is when the workup becomes the reason a seriously ill patient goes untreated, or when the familiar explanation is accepted without any workup at all.

What Guidelines Expect Once Pneumonitis Is Suspected

When a patient on a checkpoint inhibitor reports new respiratory symptoms, the expected response includes:

• checking oxygen saturation

• getting a chest CT

• testing for infection, which for grade 2 and above usually means a nasal swab and sputum, blood, and urine cultures

A bronchoscopy may follow in some cases. Our page on how lung cancer is diagnosed explains how CT and bronchoscopy are used.

Treatment follows a severity grade. Under the American Society of Clinical Oncology guideline, as summarized by MDCalc’s ASCO pneumonitis tool:

Grade	What it looks like	Expected response
1	No symptoms; changes on imaging in under 25% of the lung	Hold immunotherapy and repeat imaging. If no improvement, treat as grade 2.
2	Symptoms limiting daily activities; 25% to 50% of the lung	Hold immunotherapy, start prednisone 1 to 2 mg/kg a day, and test for infection. If no improvement in 48 to 72 hours, treat as grade 3.
3	Severe symptoms, oxygen needed, hospitalization; over 50% of the lung	Permanently stop immunotherapy and give IV steroids at 1 to 2 mg/kg a day.
4	Life-threatening breathing compromise, such as needing intubation	Same as grade 3. If no improvement after 48 hours, add infliximab, mycophenolate, IVIG, or cyclophosphamide.

Once the patient improves, steroids are tapered over 4 to 6 weeks, because stopping too fast can let the inflammation return.

These timelines matter legally. They define what a careful team does at each step, and how long it waits before escalating.

When a Missed Diagnosis Becomes Malpractice in New York

Pneumonitis is a disclosed risk of these drugs and can happen even with excellent care. A New York claim requires showing that the care departed from accepted standards and that the delay itself, not the cancer or the drug, was a substantial factor in causing additional harm.

In practice, the questions are concrete:

• Was the patient told to report new breathing symptoms?

• When symptoms were reported, was there an oxygen check, an exam, and a CT, or only reassurance?

• Was the CT read accurately?

• Was immunotherapy held and steroid treatment started as the guideline calls for?

• Did the team escalate when the patient didn’t improve within the expected window?

Causation is the hardest element. The claim has to show that earlier recognition and treatment would more likely than not have prevented the worse outcome, such as respiratory failure, intubation, an ICU stay, or death.

The defense will often argue the symptoms were too nonspecific to flag, that COPD or cancer drove the decline, or that steroids wouldn’t have changed a fast-moving case.

These cases depend on oncology and pulmonology experts, and a complaint must be filed with a certificate of merit.

A claim that the drug itself was defective is generally difficult, because the label warns of pneumonitis. The realistic claim is about monitoring, evaluation, and treatment. If the risk was never explained before treatment started, an informed consent claim under Public Health Law § 2805-d may also apply.

New York’s Filing Deadlines

Under CPLR 214-a, most malpractice claims must be filed within two years and six months of the act or omission. This is a missed treatment complication, not a missed cancer diagnosis, so the special discovery rule for failure-to-diagnose-cancer claims (Lavern’s Law) generally doesn’t apply.

The continuous treatment doctrine can extend the window for a patient who stays under the same provider’s care for the same condition, but it’s fact-specific.

Claims against public hospitals, such as NYC Health + Hospitals, require a notice of claim within 90 days. If a patient has died, the estate’s personal representative generally must file a wrongful death claim within two years of the date of death.

Talk With a New York Cancer Lawyer

If someone on immunotherapy reported new breathing problems and was reassured, sent home, or treated too slowly, Porter Law Group can review what happened.

Our New York cancer lawyers work with oncology and pulmonology experts to build the timeline and test whether a faster response would have changed the outcome. For more on these claims, see our lung cancer malpractice overview and our results in cancer cases.

Call 833-888-LATE, email info@porterlawteam.com, or request a free case evaluation.

Attorney advertising. This article provides general information and is not legal or medical advice. If you are having trouble breathing, seek emergency care right away. Prior results do not guarantee a similar outcome. Filing deadlines depend on the facts of each case.

Frequently Asked Questions

What are the early symptoms of immunotherapy pneumonitis?

The most common early signs are a new or worsening dry cough, shortness of breath, breathlessness with activities that used to be easy, chest tightness, fatigue, and a low-grade fever. Some patients have no symptoms, and the problem shows up first on a routine scan. Anyone on immunotherapy should report new breathing changes to their oncology team the same day.

Why is immunotherapy pneumonitis often mistaken for COPD or cancer progression?

Its symptoms overlap almost completely with conditions lung cancer patients already have: COPD flares, tumor growth, infections, radiation pneumonitis, heart failure, and blood clots. Because pneumonitis is partly a diagnosis of exclusion, clinicians can settle on the familiar explanation. The guideline response is an oxygen check, a chest CT, and infection testing, not reassurance.

How is immunotherapy pneumonitis treated?

Treatment follows severity. Under ASCO guidance, grade 2 means holding immunotherapy and starting prednisone 1 to 2 mg/kg a day. Grades 3 and 4 mean permanently stopping the drug and giving IV steroids. If there’s no improvement in about 48 hours, doctors add drugs like infliximab or mycophenolate. Steroids are then tapered over 4 to 6 weeks.

Can pneumonitis develop months after starting immunotherapy?

Yes. Pneumonitis often appears in the first few months, but it can show up within days of the first dose, after a year or more of treatment, or even after immunotherapy has stopped. That unpredictability is why new respiratory symptoms deserve prompt evaluation at any point in treatment, not just early on.

Can I sue if the ER sent me home and it turned out to be immunotherapy pneumonitis?

Possibly. A claim may exist if a patient on active immunotherapy was discharged without an oxygen check, CT, or consideration of pneumonitis, and the delay led to a worse outcome such as respiratory failure or an ICU stay. Most New York malpractice claims must be filed within two and a half years, and public hospital claims need a 90-day notice.