Version July 2025
INTRODUCTION —
Immune checkpoint inhibitors (ICIs) (table 1) are integrated into standard therapy for a variety of cancers. ICIs are a form of immunotherapy that enhances a patient's immune response to detect and eliminate cancer cells. However, ICIs may also cause immune-related adverse events (irAEs; ie, immune-related toxicities) of varying severity that can affect virtually any organ system. Some irAEs, such as pneumonitis, are sometimes serious and can even be fatal. Although "pneumonitis" is a general term referring to inflammation of the lungs due to varying etiologies, the term "ICI pneumonitis," in the context of this topic, refers specifically to a noninfectious inflammation process in the lungs that is caused by an ICI.
The pathogenesis, epidemiology, clinical presentation, diagnosis, and management of ICI pneumonitis are presented here. ICI toxicities in other organ systems are discussed separately.
●(See "Overview of toxicities associated with immune checkpoint inhibitors".)
●(See "Immune checkpoint inhibitor colitis".)
●(See "Rheumatologic complications of checkpoint inhibitor immunotherapy".)
The evaluation and treatment of pulmonary toxicity associated with other systemic chemotherapy or molecularly targeted antineoplastic agents, as well as radiation therapy, are discussed separately.
●(See "Pulmonary toxicity associated with chemotherapy and other cytotoxic agents".)
●(See "Pulmonary toxicity of molecularly targeted agents for cancer therapy".)
●(See "Radiation-induced lung injury".)
Additional agents with high rates and specific patterns of pulmonary toxicity are also detailed separately.
●(See "Bleomycin-induced lung injury".)
●(See "Mitomycin pulmonary toxicity".)
●(See "Cyclophosphamide pulmonary toxicity".)
●(See "Taxane-induced pulmonary toxicity".)
●(See "Methotrexate-induced lung injury".)
●(See "Busulfan-induced pulmonary injury".)
●(See "Chlorambucil-induced pulmonary injury".)
●(See "Nitrosourea-induced pulmonary injury".)
PATHOGENESIS —
ICI pneumonitis is due to immune system activation that mimics other idiopathic and autoimmune inflammatory pulmonary diseases. Other than autoimmunity, no specific mechanism or distinguishing features of ICI pneumonitis have yet been discovered.
ICI medications activate the adaptive immune response by inhibiting the programmed cell death receptor 1 and cytotoxic T lymphocyte-associated antigen 4 pathways, among other immune checkpoint molecule targets (table 1). The ultimate goal is to stimulate and enhance the antineoplastic and cytotoxic activity of T-lymphocytes, which normally play an important role in cancer surveillance. This hyperactivation of the immune response, however, can have unintended consequences with multiorgan system immune-related adverse events (irAEs). (See "Principles of cancer immunotherapy".)
As might be expected based on its mechanism of action, ICI toxicity can impact any organ that is exposed to environmental antigens/mutagens (eg, thyroid, heart, gastrointestinal tract, liver, lung, skin) and tends to mimic inflammation seen in autoimmune disorders. (See "Overview of toxicities associated with immune checkpoint inhibitors".)
In the lungs, ICIs can lead to a variety of radiologic and histologic patterns of inflammation otherwise seen idiopathically or in the setting of autoimmune disease. These include cryptogenic organizing pneumonia, nonspecific interstitial pneumonitis, hypersensitivity pneumonitis, and acute interstitial pneumonitis [1,2]. (See 'Diagnostic evaluation' below.)
The exact mechanism of ICI pneumonitis is not completely understood. Studies suggest that ICI pneumonitis develops because of an immune response to epitopes distinct from those targeted on the cancer cell; this phenomenon, which is known as 'epitope spreading,' may lead to pneumonitis as well as other organ involvement [3]. Compared with patients treated with ICIs who do not develop pneumonitis, patients with ICI pneumonitis have upregulation of lymphocytes and proinflammatory cells, and downregulation of anti-inflammatory cells in their bronchoalveolar space [4]. Cytokines present in bronchoalveolar fluid exhibit a proinflammatory and chemoattractant pattern, especially in those with steroid-refractory ICI pneumonitis. However, these findings are not specific to ICI pneumonitis; no clinically useful features have been found to distinguish ICI pneumonitis from other inflammatory processes in the lung.
EPIDEMIOLOGY AND RISK FACTORS —
ICI pneumonitis is an uncommon immune-related adverse event (irAE), with an estimated incidence of 5 percent among all patients receiving ICI therapy [1,5-13]. The risk of ICI pneumonitis varies based on specific clinical risk factors, such as (table 2) [5-7]:
●ICI regimen – The incidence of ICI pneumonitis is lower in patients treated with programmed cell death receptor 1 or programmed cell death ligand 1 inhibitors (3 to 4 percent) versus those treated with an ICI combination that includes a cytotoxic T lymphocyte-associated antigen 4 inhibitor (7 to 10 percent) [1,10,14-16].
●Cancer type – Patients with non-small cell lung cancer or renal cell carcinoma are at higher risk of developing ICI pneumonitis compared with patients with melanoma who receive similar ICI regimens [8].
●Other risk factors – Other risk factors include male sex [5], pre-existing lung disease [17,18] or interstitial lung abnormalities [19-21], autoimmune disease, smoking or tobacco use, and prior thoracic radiation therapy [22-24]. (See "Overview of toxicities associated with immune checkpoint inhibitors", section on 'Pre-existing autoimmune disease' and "Interstitial lung abnormalities".)
For patients receiving ICI therapy, the development of irAEs has generally been associated with improved antitumor efficacy across many cancer types; however, the type and severity of the irAE are still relevant to those outcomes. Because of its life-threatening nature, ICI pneumonitis is generally associated with worsened overall survival [25]. (See "Overview of toxicities associated with immune checkpoint inhibitors", section on 'Relationship between immunotherapy toxicities and efficacy'.)
CLINICAL PRESENTATION
Clinical symptoms — Patients with ICI pneumonitis most commonly present with dyspnea and cough (53 and 35 percent, respectively), while approximately one-third of patients are asymptomatic [10]. In asymptomatic patients, ICI pneumonitis is typically identified on imaging studies obtained for other indications (eg, assessing treatment response), physical examination (eg, crackles), or pulse oximetry (eg, falling oxygen saturation). Less common symptoms include fever and chest pain. More than one-half of patients will also have concurrent immune-related adverse events (irAEs) of other organ systems, such as colitis, dermatologic or mucosal toxicity, or thyroiditis. (See "Immune checkpoint inhibitor colitis" and "Overview of toxicities associated with immune checkpoint inhibitors".)
For patients actively receiving ICI therapy, the median time to onset of ICI pneumonitis is three months, but the range varies widely (between 9 days and 19 months). ICI pneumonitis may present earlier in patients treated with combination immunotherapy relative to those treated with single-agent immunotherapy (median time to onset three versus five months) [1]. Highly delayed presentations (more than one year after initiating treatment) are less common, but they occur in 10 to 15 percent of cases. In rare circumstances, new diagnoses of ICI pneumonitis have also been reported several months after ICI therapy was completed [26,27]. Radiation recall after completion of ICI therapy has also been reported [28,29].
The severity of ICI pneumonitis is generally graded based on the Common Terminology Criteria for Adverse Events (CTCAE) (table 3) although the lower grades in this system are highly subjective. Presentations without symptoms or with mild disability (grades 1 and 2 toxicity) are more common than presentations including hypoxemia or likely hospitalization (grades 3 and 4) [1]. Although fatalities due to ICIs (grade 5 toxicity) are rare (0.8 to 1.7 percent), pneumonitis had the largest proportion of ICI-related deaths (21 percent) in one meta-analysis [30].
Physical examination — On physical examination, typical findings include crackles on auscultation or evidence of lung consolidation (eg, loss of adventitious sounds, egophony, dullness to chest percussion). Ambulatory pulse oximetry or a formal six-minute walk test may detect decreases in oxygen saturation (due to a loss of diffusing capacity related to the ICI pneumonitis) that may not be clinically evident in the resting patient.
DIAGNOSTIC EVALUATION —
The diagnosis of ICI pneumonitis is based on a history of treatment with ICIs, clinical and radiographic findings consistent with acute parenchymal inflammation of the lungs, and exclusion of other potential causes of pneumonitis. While there are no specific clinical, radiographic, or histopathologic findings that are diagnostic for ICI pneumonitis, such studies can be used to guide the diagnostic evaluation and to exclude other causes of pneumonitis. (See 'Differential diagnosis' below.)
When to suspect the diagnosis — The diagnosis of ICI pneumonitis should be suspected in patients who are receiving (or have recently received) ICI therapy and who present with new or worsening pulmonary symptoms (eg, shortness of breath, dyspnea on exertion, or falling oxygen saturation). ICI pneumonitis may also be suspected in asymptomatic patients with recent ICI therapy with new radiologic findings consistent with pneumonitis. Although ICI pneumonitis can occur at any time during or even after therapy, clinical suspicion should be highest during the first several months of treatment. For patients with grade 2 to 4 symptoms (table 3), consultation with a pulmonologist should be obtained to assist with diagnostic evaluation, monitoring, and selection of therapy [31]. (See 'Management' below.)
Imaging studies — For patients with a clinical presentation suspicious for ICI pneumonitis, the most important step in the initial diagnostic evaluation is to obtain a high-resolution computed tomography (CT) scan of the chest (with or without contrast) [32]. A chest CT can demonstrate several radiographic patterns associated with ICI pneumonitis, although there is no one specific radiographic feature for this condition (figure 1). A contrast-enhanced chest CT can also assess for other potential diagnoses, such as pulmonary embolism or malignant pulmonary infiltration. ICI pneumonitis should be radiographically evident, so lack of inflammatory changes on a chest CT excludes the diagnosis.
For patients being evaluated for ICI pneumonitis in the outpatient setting, such as a medical oncology clinic, who do not have immediate access to CT imaging, a chest radiograph (CXR) can be used to guide the initial diagnostic evaluation. A CXR can be rapidly obtained and may be sufficient to suggest the possibility of ICI pneumonitis and direct the clinician to obtain further diagnostic evaluation (such as a chest CT). However, a CXR alone is generally not able to exclude the diagnosis, as some radiographic findings of ICI pneumonitis may be subtle and below the detection of a plain film radiograph. In observational studies, a CXR did not detect new radiographic abnormalities in approximately one-fourth of patients with ICI pneumonitis [1,33-35].
Radiographic patterns of ICI pneumonitis (table 1) are variable. The most common radiographic pattern on chest CT is organizing pneumonia (40 to 50 percent), followed by nonspecific interstitial pneumonitis [8,36]. Other radiographic patterns, however, have also been described and include bronchiolitis, hypersensitivity pneumonitis, and acute interstitial pneumonitis. Pleural effusions are rare but have been observed [12]. (See "Diagnostic evaluation of the hemodynamically stable adult with a pleural effusion", section on 'History and examination'.)
Radiation recall pneumonitis (ie, recurrent inflammation confined to a prior radiation field) has also been described [28,29]. This phenomenon can occur even when treatment is initiated years after radiation therapy.
Additional evaluation — In select patients, additional evaluation may be used to exclude alternative causes of pulmonary symptoms. (See 'Differential diagnosis' below.)
●Infectious workup – If imaging studies or other clinical findings indicate the possibility of a pulmonary infection, an initial infectious workup can be obtained, such as a nasal swab for respiratory viral panels and sputum cultures [31,37]. Other infectious workups may also be appropriate, depending upon the suspected pathogen. (See 'Differential diagnosis' below.)
●Pulmonary function testing – For patients whose symptoms are mild enough to obtain reliable data, pulmonary function testing with spirometry and diffusion capacity can help quantify the severity of the disease and may sometimes assist in determining alternative explanations for new pulmonary symptoms (eg, exacerbations of obstructive lung disease). ICI pneumonitis typically results in restriction and a reduction in diffusion capacity. A six-minute walk test may also be appropriate to assess the degree of pulmonary functional impairment on a case-by-case basis.
●What is the role of bronchoscopy? – Bronchoscopy is not usually necessary for the diagnosis of ICI pneumonitis; its use is typically reserved for patients with grade 2 or higher pneumonitis (table 3) whose diagnosis remains uncertain after an initial evaluation or whose symptoms are unresponsive to initial management. Bronchoscopy with bronchoalveolar lavage and/or transbronchial biopsy may be used in selected patients to exclude alternative causes of pneumonitis, including infection, cancer progression, alveolar hemorrhage, and sarcoid-like reactions. If necessary, the lung tissue obtained from lavage and/or biopsy can also be used on a case-by-case basis to clarify a suspected diagnosis (eg, distinguishing infection from progressive cancer) [33,34,38]. (See 'Differential diagnosis' below.)
The histopathologic features for ICI pneumonitis are diverse and there is no one pathognomic finding. In one observational study that included 27 patients with ICI pneumonitis who underwent lung biopsy, histopathologic findings included cellular interstitial pneumonitis, organizing pneumonia, diffuse alveolar damage, or no abnormalities [1]. Interstitial inflammatory infiltrates included poorly formed granulomas or eosinophils. This lack of diagnostic histologic pattern means that biopsy is rarely justified unless necessary for an alternative diagnosis.
DIFFERENTIAL DIAGNOSIS —
The differential diagnosis of ICI pneumonitis is broad and includes infection, exacerbations of obstructive lung disease, other causes of noninfectious pneumonitis, pulmonary edema, pulmonary embolism, cancer progression, and pulmonary hemorrhage. In a meta-analysis of patients with treatment-related adverse events from programmed cell death receptor 1 and programmed cell death ligand 1 inhibitors, 20 percent of deaths were attributed to respiratory events other than pneumonitis [30].
●Pneumonia – Pulmonary parenchymal infection is a frequent alternative diagnosis, particularly in those with more severe symptoms (grade 3 or 4 disease (table 3)). In one retrospective study of infectious complications after ICI therapy for solid organ malignancies, pneumonia was identified as frequently as ICI pneumonitis [39]. Empiric antibiotic therapy, if given, is typically tailored to the patient's immune status and prior infectious complications; atypical pathogens such as cytomegalovirus and pneumocystis jirovecii have been reported [40,41]. The infectious workup often includes sputum culture, respiratory viral panels, and/or invasive sampling via bronchoscopy to rule out or identify infectious agents. (See "Overview of community-acquired pneumonia in adults" and "Overview of diagnostic tests for cytomegalovirus infection" and "Epidemiology, clinical presentation, and diagnosis of Pneumocystis pulmonary infection in patients with HIV".)
●Exacerbations of obstructive lung disease – Patients with worsening pulmonary symptoms but without radiographic findings suggestive of acute pulmonary parenchymal inflammation do not have ICI pneumonitis but may be suffering from an exacerbation of chronic obstructive pulmonary disease (COPD) or asthma. COPD exacerbation as a consequence of immunotherapy is biologically plausible and likely underrecognized [42]. (See "Chronic obstructive pulmonary disease: Diagnosis and staging" and "Asthma in adolescents and adults: Evaluation and diagnosis".)
●Sarcoid-like reactions – Sarcoid-like granulomatous pulmonary reactions are also a potential consequence of ICI therapy and can appear similar to ICI pneumonitis on clinical examination and imaging. Common features include subpleural micronodular opacities and hilar lymphadenopathy. Patients may be asymptomatic or present with cough, wheeze, fatigue, or chest pain. Skin findings (subcutaneous or papular sarcoidosis) are also common. Although occasionally imaging findings are sufficiently characteristic, a biopsy is frequently needed to confirm the diagnosis. Cessation of ICI with or without systemic treatment with glucocorticoids may be needed in more severe cases, but are unnecessary in asymptomatic or minimally symptomatic patients [43]. (See "Clinical manifestations and diagnosis of sarcoidosis".)
●Cancer progression – Progression of the underlying malignancy, particularly lymphangitic spread in the lung or postobstructive complications from primary lung cancer or large metastases, can result in pulmonary symptoms and imaging findings that resemble ICI pneumonitis. Depending on the cancer type, extrathoracic imaging studies and/or tumor markers can be used to assess for progressive disease. In selected cases, bronchoscopy and/or biopsy of the affected lung tissue may be diagnostic for disease progression. Of note, cancer progression despite ICI therapy is different from pseudoprogression, a pattern of ICI treatment response, which is discussed separately. (See "Principles of cancer immunotherapy", section on 'Patterns of response'.)
●Interstitial lung diseases – New or progressive interstitial lung disease (ILD) in a patient on ICI therapy can mimic ICI pneumonitis. No specific radiologic patterns can distinguish between ICI toxicity and idiopathic ILDs. Occasionally, systemic flares of connective tissue diseases associated with worsening ILD may be treated with specific disease-modifying antirheumatic drugs rather than with changes in ICI therapy. Otherwise, new or worsening ILD while on an ICI is typically treated as ICI toxicity. (See "Approach to the adult with interstitial lung disease: Diagnostic testing".)
●Drug-induced pneumonitis due to coadministered antineoplastic agents – ICI therapies are increasingly being used in combination with other antineoplastic agents (such as chemotherapy and molecularly targeted agents), which can also potentially cause drug-induced pneumonitis. (See "Pulmonary toxicity associated with systemic antineoplastic therapy: Clinical presentation, diagnosis, and treatment".)
While all agents are typically held for moderate to severe toxicity, it is important to determine the causative agent because it impacts the selection of future cancer therapy. Typically, if drug-induced pneumonitis is suspected, the causative agent is determined clinically based on the likelihood of pneumonitis with each agent, the specific clinical presentation (which may be more consistent with one agent than the other), and the presence of other concomitant immune-related adverse events (irAEs).
●Other conditions, including other ICI toxicities – For patients with dyspnea but without pulmonary inflammation on chest imaging, pulmonary embolism is a common etiology. Pulmonary edema can mimic pneumonitis and is more common in those with pre-existing cardiovascular disease. (See "Clinical presentation and diagnostic evaluation of the nonpregnant adult with suspected acute pulmonary embolism" and "Approach to diagnosis and evaluation of acute decompensated heart failure in adults".)
Pulmonary hemorrhage can also result in ground glass infiltrates; it is most frequently associated with diastolic heart failure, bleeding disorders, and anticoagulant therapy. In addition, other potential causes of immunotherapy toxicities may lead to respiratory symptoms or compromise including ICI-related myocarditis, thyroiditis, hypophysitis, and myasthenia gravis. (See "Overview of toxicities associated with immune checkpoint inhibitors" and "The diffuse alveolar hemorrhage syndromes", section on 'Bland pulmonary hemorrhage'.)
MANAGEMENT —
The management of ICI pneumonitis is guided by the severity of the initial symptoms and degree of pulmonary impairment, generally based on Common Terminology Criteria for Adverse Events (CTCAE) grade (table 3 and algorithm 1). Therapeutic options range from close observation for clinical worsening to permanent withdrawal of ICI therapy and a prolonged course of systemic immunosuppressive therapy. This approach is generally consistent with clinical practice guidelines for the management of ICI-related toxicities from the American Society of Clinical Oncology (ASCO), European Society of Medical Oncology (ESMO), National Comprehensive Cancer Network (NCCN), and the Society for Immunotherapy of Cancer (SITC) [38,44-46].
Initial management
No symptoms (grade 1) — Patients who are asymptomatic and whose disease is detected clinically or on imaging studies only (grade 1 pneumonitis) (table 3) should be observed over a period of three to four weeks. We do not initiate treatment with systemic glucocorticoids. ICI therapy is also held temporarily for most patients. However, continuing ICI therapy is also an option based on the need to continue such therapy for cancer control and a risk-benefit discussion with the patient. Although practice is variable, patients on observation may be clinically monitored by history and physical examination every two to four weeks (or weekly if continuing ICI therapy), home or office pulse oximetry, and a follow-up chest CT in three to four weeks (or sooner if progressive symptoms).
Patients whose clinical findings (eg, physical examination and imaging studies) are stable or improve/resolve may be evaluated for reinitiation of ICI therapy. (See 'Resuming immune checkpoint inhibitors' below.)
Patients who develop worsening symptoms and/or significant disease progression on imaging studies are initiated on therapy based on the severity of their symptoms. (See 'Mild to moderate symptoms (grade 2)' below and 'Severe or life-threatening symptoms (grade 3 or 4)' below.)
Mild to moderate symptoms (grade 2) — Most patients with mild to moderate symptoms (grade 2) of ICI pneumonitis (table 3) can be managed in the outpatient setting [1].
●For patients with grade 2 symptoms, we hold ICI therapy.
●We also suggest initiating systemic glucocorticoids rather than observation or other systemic agents. Although clinical practice varies, we begin oral prednisone at a dose of 0.5 to 1 mg/kg/day based on actual body weight (to a maximum dose of 80 to 120 mg daily), or an equivalent agent, depending on the severity of symptoms. Patients should be monitored every three to seven days for changes in clinical symptoms.
●We obtain a pulmonary consultation to assist with further diagnostic workup and monitoring, as disease severity can rapidly escalate without the necessary therapy. (See 'Differential diagnosis' above.)
●For patients where a respiratory infection has not been excluded or for whom cultures are pending, we also treat with empiric antibiotics for community acquired pneumonia. (See "Overview of community-acquired pneumonia in adults".)
If symptoms worsen within 48 to 72 hours despite initiating oral glucocorticoid therapy, patients are treated using the same approach as those with initial grade 3 pneumonitis, including evaluation for alternative diagnoses. The dose of systemic glucocorticoids should also be increased to 2 mg/kg/day in this setting. (See 'Severe or life-threatening symptoms (grade 3 or 4)' below and 'Differential diagnosis' above.)
Patients with stable symptoms on oral glucocorticoids over 48 to 72 hours may have a condition called chronic pneumonitis. They can either continue the current dose of oral glucocorticoids or escalate the dose of oral prednisone to 1 to 2 mg/kg/day, with continued reevaluation of symptoms. (See 'Chronic ICI pneumonitis' below.)
Patients whose symptoms improve or resolve with oral glucocorticoids (typically over three to seven days) may begin to taper therapy. We gradually taper prednisone by 10 mg every five to seven days with the goal of discontinuing prednisone over four to six weeks. If clinical symptoms or imaging studies significantly worsen during the taper, we return to the most recently well-tolerated dose of prednisone (or equivalent glucocorticoid) for two weeks prior to resuming tapering. Interval chest CT imaging is helpful to assess for response or worsening symptoms; imaging can be obtained every four to six weeks initially, and then every 8 to 12 weeks until the resolution of symptoms. Resuming ICI therapy upon resolution of symptoms is discussed separately. (See 'Resuming immune checkpoint inhibitors' below.)
Patients who receive a prednisone taper should be given appropriate antimicrobial, antiviral, and antifungal prophylaxis per institutional guidelines. Pneumocystis pneumonia prophylaxis is given to patients receiving the equivalent of oral prednisone at a dose of 20 mg daily for one month or longer. Further details are discussed separately. (See "Treatment and prevention of Pneumocystis pneumonia in patients without HIV", section on 'Prophylaxis' and "Overview of toxicities associated with immune checkpoint inhibitors", section on 'Risk with immunosuppressive therapy'.)
Severe or life-threatening symptoms (grade 3 or 4) — Patients with severe (grade 3) or life-threatening (grade 4) symptoms of ICI pneumonitis (table 3) require inpatient hospital admission for monitoring and diagnostic workup.
●For patients with grade 3 or 4 symptoms, we immediately hold ICI therapy.
●We initiate treatment with intravenous (IV) glucocorticoids. Although dosing may vary based on institutional guidelines and disease severity, we administer IV methylprednisolone either at a dose of 1 to 2 mg/kg/day or at a pulse dose of 500 to 1000 mg daily (divided into two daily doses) for three days followed by a maintenance dose of 1 to 2 mg/kg/day.
●Pulmonary consultation is necessary for evaluation.
●Patients should receive a thorough infectious workup, typically including a respiratory nasal swab and sputum culture. Bronchoscopy with bronchoalveolar lavage is frequently appropriate to rule out atypical infections and malignant lung infiltration. We typically treat with empiric antibiotics until infection has been excluded. This may include coverage for less typical pathogens (eg, Pneumocystis jirovecii, Pseudomonas aeruginosa) depending on the degree of patient immunocompromise and other individual patient characteristics. (See "Approach to the immunocompromised patient with fever and pulmonary infiltrates", section on 'Infection' and "Treatment of community-acquired pneumonia in adults who require hospitalization" and "Treatment and prevention of Pneumocystis pneumonia in patients without HIV".)
●Additional diagnostic evaluation for other alternative etiologies of pneumonitis should also be pursued. (See 'Differential diagnosis' above.)
Patients whose symptoms do not improve with IV glucocorticoids are treated for steroid-refractory ICI pneumonitis. (See 'Management of steroid-refractory disease' below.)
For patients whose symptoms improve to grade 2 or less, we discontinue IV glucocorticoids and begin an equivalent dose using an oral formulation, such as prednisone, prior to hospital discharge. Oral glucocorticoid tapers may continue as an outpatient.
●Time to clinical improvement is variable and can be seen as soon as 42 to 78 hours in some patients and as long as 7 to 14 days in others. Clinical stability often occurs first and is reassuring, particularly when the initial clinical deterioration was rapid.
●We gradually taper prednisone by 10 mg every five to seven days, typically over four to eight weeks; the tapering schedule depends upon the robustness of the initial glucocorticoid response, pace of improvement, and severity of glucocorticoid-related adverse effects. If symptoms or imaging studies significantly worsen during the taper, we return to the most recently well-tolerated dose of prednisone (or equivalent) for two weeks prior to resuming tapering. Pulmonary function testing with spirometry and diffusing capacity as well as interval chest CT imaging are helpful for assessment of response or for worsening symptoms. Resuming ICI therapy is discussed separately. (See 'Resuming immune checkpoint inhibitors' below.)
●Patients who receive a prednisone taper should be given appropriate antimicrobial, antiviral, and antifungal prophylaxis per institutional guidelines. Pneumocystis pneumonia prophylaxis is given to patients receiving the equivalent of oral prednisone at a dose of 20 mg daily for one month or longer. Further details are discussed separately. (See "Treatment and prevention of Pneumocystis pneumonia in patients without HIV", section on 'Prophylaxis' and "Overview of toxicities associated with immune checkpoint inhibitors", section on 'Risk with immunosuppressive therapy'.)
Management of steroid-refractory disease — For patients with grade 3 to 4 ICI pneumonitis who fail to improve after a trial of systemic glucocorticoids (ie, steroid-refractory pneumonitis), we suggest the addition of a second-line immunosuppressive agent to systemic glucocorticoids. The optimal second-line agent is not established and is based on the preference of the treating clinician. Potential options include intravenous immune globulin (IVIG), infliximab, mycophenolate mofetil, cyclophosphamide, azathioprine, and tocilizumab.
Steroid-refractory pneumonitis refers to ICI pneumonitis that derives no clinical benefit from systemic glucocorticoids [47-51]. This condition occurs in approximately 10 to 20 percent of patients with moderate to severe ICI pneumonitis [48,50]. Such patients often require intensive care unit level of care and have a guarded prognosis. If not performed already, patients with suspected steroid-refractory pneumonitis should undergo a thorough diagnostic evaluation for alternative etiologies including malignant lung infiltration, infection, an alternate pneumotoxic drug, or radiation pneumonitis, among other conditions. (See 'Differential diagnosis' above.)
Steroid-refractory pneumonitis should be distinguished from steroid-resistant pneumonitis, in which patients with ICI pneumonitis initially respond to glucocorticoids but symptoms do not resolve (ie, subsequently develop recurrent pneumonitis in the context of glucocorticoid tapering and no ICI rechallenge) [49]. A SITC Expert Panel has developed consensus definitions to reclassify immune-related adverse events (irAE), including pneumonitis, according to glucocorticoid responsiveness [51], but this system is not in widespread use. (See 'Chronic ICI pneumonitis' below.)
Several second-line immunosuppressants have been evaluated for steroid-refractory pneumonitis, but the data are limited for the optimal therapy. We use IVIG, which is administered at either 0.4 g/kg daily for five consecutive days or 1 g/kg daily for two consecutive days. Both dosing strategies provide for a total of 2 g/kg in divided doses, and either strategy is appropriate. IVIG has a relatively rapid onset of action, which is necessary given the severity of the disease. In addition, limited observational data also suggest that IVIG is associated with lower mortality rates compared with infliximab [48,52].
Other second-line immunosuppressive regimens include:
●Infliximab [1,47]
●Mycophenolate mofetil [49]
●Intravenous (IV) cyclophosphamide [50]
●Azathioprine [32]
●Tocilizumab [53]
There have also been case reports of short-term or longer-term improvement with the use of nintedanib, the multikinase inhibitor targeting vascular endothelial growth factor, platelet-derived growth factor receptor, and fibroblast growth factor receptor, in the management of ICI pneumonitis [54,55].
The prognosis for steroid-refractory pneumonitis is extremely poor. In a retrospective study of 26 patients with ICI pneumonitis (primary steroid-refractory = 12, steroid-resistant = 14) requiring additional immunosuppressive therapy, all 12 patients with steroid-refractory disease died, with the cause of death attributable to pneumonitis or infectious complications [49].
CLINICAL COURSE FOLLOWING THERAPY
Typical ICI pneumonitis — Most patients with ICI pneumonitis improve with glucocorticoids, experience resolution of symptoms, and successfully complete an oral glucocorticoid taper over several weeks. Some patients, particularly those with pre-existing lung disease, may develop residual scarring along with mild reduction in pulmonary function. However, the absence of pulmonary inflammation is associated with dramatically diminished symptoms, except in severe cases. Residual dry cough is the most common persistent symptom of ICI pneumonitis and is often difficult to treat.
Chronic ICI pneumonitis — Chronic ICI pneumonitis is defined as long-term, steroid-dependent pneumonitis that stabilizes or diminishes with initial glucocorticoid therapy but worsens upon tapering of the glucocorticoid, requiring 12 weeks or more of immunosuppressive therapy after discontinuing ICI therapy [51]. In a retrospective analysis of 299 patients with non-small cell lung cancer and melanoma treated with ICI therapy, the overall incidence of chronic ICI pneumonitis was 2 percent; the condition also seemed to be more common in those with a prolonged course of ICI therapy (median onset 12 months after ICI initiation) [56]. On imaging studies, chronic pneumonitis most commonly has an organizing pneumonia-like appearance. Prolonged ICI course and an organizing pneumonia pattern were also found to be risk factors for recurrent symptoms on steroid tapering in a prospective study [57].
For patients with chronic ICI pneumonitis, we resume prior glucocorticoid doses when symptoms flare during tapering. Further management includes the addition of a second immunosuppressive agent to minimize ongoing glucocorticoid exposure and treat the underlying inflammation, using a similar approach to the management of cryptogenic organizing pneumonia. Options for additional immunosuppression include infliximab and mycophenolate mofetil. However, studies using this approach show variable success, with only 50 percent of cases demonstrating eventual resolution of pneumonitis [56]. (See "Cryptogenic organizing pneumonia", section on 'Glucocorticoid-sparing agents for recurrent relapses or glucocorticoid intolerance'.)
Recurrent ICI pneumonitis — Recurrent ICI pneumonitis is defined as an additional episode of ICI pneumonitis after complete clinical and radiologic resolution of the previous episode. This condition can occur upon reintroduction of ICI therapy (provoked) or despite complete discontinuation of ICI therapy (unprovoked). In a retrospective analysis, ICI pneumonitis recurred in 6 of 19 cases of ICI pneumonitis [58].
We manage recurrent ICI pneumonitis similar to new-onset ICI pneumonitis, with the exception that recurrent toxicity is a contraindication to rechallenge with ICI therapy in almost all cases. (See 'Resuming immune checkpoint inhibitors' below.)
RESUMING IMMUNE CHECKPOINT INHIBITORS —
The decision to resume immune checkpoint inhibitor (ICI) therapy mainly depends on the severity of the initial episode (table 3), resolution of pneumonitis, and the likelihood of benefit.
●Resolved grade 1 pneumonitis – Patients with grade 1 ICI pneumonitis that completely resolves clinically and radiographically may safely resume ICI therapy, if it was temporarily held as part of management.
●Resolved mild to moderate (grade 2) or severe (grade 3) pneumonitis – For patients with mild to moderate (grade 2) or severe (grade 3) ICI pneumonitis that completely resolves clinically and radiographically, the decision to resume ICI therapy requires careful balancing of the risks and benefits, based on individual patient factors and shared-decision making between the medical oncologist and the patient.
The decision to retreat is based on multiple clinical factors including the severity and nature of the initial immune-related adverse events (irAE), its degree of responsiveness to systemic immunosuppression, the risk of recurrent ICI pneumonitis, the need for a cancer response, the availability of alternative cancer treatment options, and if the ICI therapy was used alone or in combination with other cancer therapies [1]. In patients who have demonstrated a response to ICI therapy and subsequently develop symptomatic ICI pneumonitis, resuming ICI therapy may not confer any additional survival advantage [59]. General principles of resuming ICI therapy after resolution of irAEs are discussed separately. (See "Overview of toxicities associated with immune checkpoint inhibitors", section on 'Retreatment after prior toxicity'.)
●Life-threatening (grade 4), chronic, or recurrent pneumonitis – ICI therapy should be permanently discontinued in patients with life-threatening disease requiring intensive care unit interventions (grade 4 pneumonitis, regardless of resolution status), those with grade 2 to 3 pneumonitis that does not resolve, and those with recurrent ICI pneumonitis (provoked or unprovoked).
SOCIETY GUIDELINE LINKS —
Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Management of toxicities due to checkpoint inhibitor immunotherapy".)
SUMMARY AND RECOMMENDATIONS
●Definition – Immune checkpoint inhibitor (ICI) pneumonitis is a noninfectious inflammation of the lungs that is caused by ICI therapy (table 1). This condition arises due to immune system activation that mimics other idiopathic and autoimmune inflammatory pulmonary diseases. (See 'Introduction' above and 'Pathogenesis' above.)
●Epidemiology – ICI pneumonitis is an uncommon immune-related adverse event (irAE), with an estimated incidence of 5 percent. The risk varies based on the ICI regimen used and cancer type, among other factors (table 2).
●Clinical presentation – Patients most commonly present with dyspnea and cough, while approximately one-third are asymptomatic. More than one-half of patients will also have concurrent irAEs of other organ systems. The severity of ICI pneumonitis is graded according to the Common Terminology Criteria for Adverse Events (CTCAE) (table 3). (See 'Clinical symptoms' above.)
●Diagnostic evaluation – The diagnosis is based on a history of treatment with ICIs, clinical and radiographic findings consistent with acute parenchymal inflammation, and exclusion of other potential causes. (See 'Diagnostic evaluation' above.)
•When to suspect the diagnosis – ICI pneumonitis should be suspected in patients actively receiving ICI therapy who present with new or worsening pulmonary symptoms (eg, shortness of breath, dyspnea on exertion, or falling oxygen saturation), or those who are asymptomatic with new radiologic findings consistent with pneumonitis (figure 1). (See 'When to suspect the diagnosis' above.)
•Imaging – The most important initial diagnostic step is to obtain a high-resolution CT scan of the chest (with or without contrast). The most common radiographic pattern is organizing pneumonia, followed by nonspecific interstitial pneumonitis (figure 1). (See 'Imaging studies' above.)
•Additional testing – Additional testing may include an initial infectious workup (eg, nasal swab for viral pathogens, sputum cultures) and pulmonary function testing. Bronchoscopy is not usually necessary for the diagnosis; its use is typically reserved for patients with grade 2 or higher pneumonitis (table 3) whose diagnosis remains uncertain after an initial evaluation or whose symptoms are unresponsive to initial management. (See 'Additional evaluation' above.)
●Differential diagnosis – The differential diagnosis is broad and includes infection, exacerbations of obstructive lung disease, sarcoid-like reactions, cancer progression, interstitial lung disease (ILD), pneumonitis due to another drug, pulmonary hemorrhage, pulmonary embolism, and pulmonary edema. (See 'Differential diagnosis' above.)
●Initial management – Management of ICI pneumonitis is guided by the severity of the initial symptoms and degree of pulmonary impairment, which is generally based on CTCAE grade (table 3 and algorithm 1).
•No symptoms (grade 1) – Patients who are asymptomatic and whose disease is detected clinically or on imaging studies only (grade 1 pneumonitis) (table 3) should be observed over a period of three to four weeks. We do not initiate treatment with systemic glucocorticoids. Although ICI therapy is usually held temporarily, continuing therapy is also an option with close monitoring. (See 'No symptoms (grade 1)' above.)
•Symptomatic disease (grade 2 to 4) – For patients with symptomatic (grades 2 to 4) pneumonitis (table 3), management is as follows:
-Hold ICI therapy.
-We suggest initiating systemic glucocorticoids rather than observation or other systemic agents (Grade 2C).
For patients with grade 2 symptoms, we begin oral prednisone at a dose of 0.5 to 1 mg/kg/day actual body weight (maximum dose of 80 to 120 mg) or an equivalent agent, although clinical practice varies. If a respiratory infection has not been excluded, we also treat with empiric antibiotics for community-acquired pneumonia. (See 'Mild to moderate symptoms (grade 2)' above.)
Patients with mild to moderate (grade 2) symptoms who worsen after 48 to 72 hours of oral glucocorticoid therapy, or those with severe (grade 3) or life-threatening (grade 4) symptoms require hospitalization. Although dosing may vary based on severity of disease and institutional guidelines, we treat with intravenous (IV) methylprednisolone either at a dose of 1 to 2 mg/kg/day or pulse dose (500 to 1000 mg daily, divided into two daily doses) for three days followed by a maintenance dose of 1 to 2 mg/kg/day. (See 'Severe or life-threatening symptoms (grade 3 or 4)' above.)
-Pulmonary consultation should be obtained for further diagnostic workup of alternative etiologies and for ongoing monitoring. (See 'Differential diagnosis' above.)
●Management of steroid-refractory disease – For patients with grade 3 to 4 symptoms who fail to improve after a trial of systemic glucocorticoids (ie, steroid-refractory disease), the prognosis is extremely poor. We suggest the addition of a second-line immunosuppressive agent to systemic glucocorticoids (Grade 2C). We use intravenous immune globulin (IVIG) due to its rapid onset of action. Other options include infliximab, mycophenolate mofetil, cyclophosphamide, azathioprine, and tocilizumab. (See 'Management of steroid-refractory disease' above.)
●Clinical course following therapy – Most patients with ICI pneumonitis improve with glucocorticoids, experience resolution of symptoms, and successfully complete an oral glucocorticoid taper over several weeks. A small percentage of patients may require prolonged immunosuppressive therapy or develop recurrent ICI pneumonitis. (See 'Management' above and 'Clinical course following therapy' above.)
●Resuming ICI therapy – The decision to resume ICI therapy mainly depends on the severity of the initial episode (table 3), resolution of pneumonitis, and the likelihood of benefit. (See 'Resuming immune checkpoint inhibitors' above.)
