ICU · oncology
Immune Checkpoint Inhibitor Toxicity in the ICU
Also known as Checkpoint inhibitor toxicity · Immune-related adverse events (irAEs) · ICI pneumonitis · ICI myocarditis · ICI colitis · Immunotherapy toxicity · Anti-PD-1 toxicity · Anti-CTLA-4 toxicity · Nivolumab toxicity · Pembrolizumab toxicity · Ipilimumab toxicity
Immune checkpoint inhibitor (ICI) toxicity — immune-related adverse events (irAEs) from CTLA-4 (ipilimumab), PD-1 (nivolumab, pembrolizumab), and PD-L1 (atezolizumab, durvalumab) inhibitors causing pneumonitis, colitis, hepatitis, endocrinopathy (thyroiditis, hypophysitis, adrenalitis), myocarditis, nephritis, neurotoxicity, and dermatological reactions. ICU presentation: respiratory failure (pneumonitis), shock (myocarditis, adrenal crisis), severe colitis with perforation, encephalitis, Guillain-Barre syndrome variant, and Stevens-Johnson syndrome. Management framework: stop ICI, grade severity (CTCAE v5.0), corticosteroids (methylprednisolone 1-2 mg/kg for grade 2; 1 g/day pulse for grade 3-4), second-line immunosuppression (infliximab for colitis, mycophenolate for hepatitis, abatacept/ruxolitinib for myocarditis, rituximab for neurologic), supportive care. Myocarditis = highest mortality (25-50%). Early recognition + prompt steroids = survival.
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Overview
Immune checkpoint inhibitors have revolutionised cancer therapy — melanoma, non-small-cell lung cancer (NSCLC), renal cell carcinoma, urothelial carcinoma, Hodgkin lymphoma, head and neck squamous cell carcinoma, and many others now have ICI as first-line therapy. With this explosion in use, irAEs are increasingly encountered in ICU practice. The intensivist must recognise the patterns, because the presentation, differential diagnosis, and management differ fundamentally from conventional chemotherapy toxicity (which is cytopenia, mucositis, neuropathy — NOT autoimmune organ inflammation). [1]
The mechanism is elegant and critical to understand: CTLA-4 is an inhibitory receptor on T-cells that acts early in T-cell activation (in lymph nodes — prevents CD28-B7 co-stimulation). PD-1 is an inhibitory receptor that acts later (in peripheral tissues — binds PD-L1/PD-L2 on target cells to suppress T-cell effector function). Blocking either removes the "brakes" on T-cell immunity — effective against tumours that exploit these checkpoints to evade immune surveillance, but also unleashing autoreactive T-cell clones against normal tissues.[1][2]
ICI agents and their toxicity profiles
| Agent | Target | Typical cancers | Distinctive toxicity |
|---|---|---|---|
| Ipilimumab | CTLA-4 | Melasma, renal cell | Colitis (most common severe irAE — 30-40% any grade), hypophysitis, pruritus |
| Tremelimumab | CTLA-4 | Mesothelioma | Colitis, hepatitis (similar to ipilimumab) |
| Nivolumab | PD-1 | Melanoma, NSCLC, RCC, HNSCC | Pneumonitis (especially NSCLC), thyroiditis |
| Pembrolizumab | PD-1 | Melanoma, NSCLC, urothelial, HNSCC, gastric | Pneumonitis, myocarditis, hepatitis |
| Cemiplimab | PD-1 | Cutaneous SCC | Pneumonitis, colitis |
| Atezolizumab | PD-L1 | Urothelial, NSCLC, TNBC | Hepatitis, pneumonitis (lower rate than anti-PD-1) |
| Durvalumab | PD-L1 | NSCLC (consolidation), bladder | Pneumonitis (common after chemoradiation) |
| Avelumab | PD-L1 | Merkel cell, renal cell | Infusion reactions (anti-PD-L1 highest rate) |
CTCAE v5.0 grading for common irAEs — determines treatment intensity
| Organ | Grade 1 (mild) | Grade 2 (moderate) | Grade 3 (severe) | Grade 4 (life-threatening) |
|---|---|---|---|---|
| Pneumonitis | Asymptomatic radiographic | Symptomatic, limits ADL | Severe dyspnoea, O2 needed | Life-threatening respiratory failure |
| Colitis | 1-3 stools/day over baseline | 4-6/day, abdominal pain | 7+ /day, perforation | Life-threatening consequences |
| Hepatitis | ALT/AST 1-3x ULN | 3-5x ULN | 5-20x ULN | >20x ULN |
| Myocarditis | — | Mild symptoms, troponin + | Heart failure, arrhythmia | Cardiogenic shock, arrest |
| Endocrinopathy | Asymptomatic lab abnormal | Symptomatic, hormone replacement | Hospitalisation required | Life-threatening crisis |
| Management | Continue ICI, monitor | Stop ICI, prednisone 1-2 mg/kg | Hospitalise, methylprednisolone 1-2 mg/kg | ICU, methylprednisolone 1 g/day, second-line |
ICI pneumonitis — the respiratory threat
ICI pneumonitis is inflammation of the lung parenchyma triggered by checkpoint inhibition. It affects 3-5% of patients on anti-PD-1/PD-L1 monotherapy and up to 10% with combination anti-CTLA-4 + anti-PD-1. Highest risk: NSCLC (pre-existing lung damage), renal cell carcinoma, and combination therapy. Median onset: 2-6 months after starting ICI (but can occur after any dose, even after discontinuation).[6]
Presentation: insidious onset of dry cough, exertional dyspnoea, and hypoxia. Fever may be present (mimics infection). Bilateral crackles on auscultation. Hypoxia can progress rapidly (grade 3-4 within 24-48 hours). Key: any new respiratory symptom in a patient on ICI = suspect pneumonitis until proven otherwise. [1]
HRCT patterns (radiological classification):
- Cryptogenic organising pneumonia (COP) pattern: peripheral/subpleural consolidation, reverse halo — MOST COMMON (good prognosis)
- Ground-glass opacities: diffuse bilateral — second most common
- Hypersensitivity pneumonitis pattern: upper-lobe predominant, centrilobular nodules
- NSIP pattern: lower-lobe predominant reticulation
- Acute interstitial pneumonia (AIP)/ARDS pattern: diffuse consolidation — worst prognosis, often requires ICU [1]
Pneumonitis management protocol — ICU-level grade 3-4
- STOP the ICI — permanently for grade 3-4 (no rechallenge)
- EXCLUDE infection — this is the #1 priority: (a) bronchoalveolar lavage (BAL) with bacterial/fungal/viral PCRs (including CMV, PCP, respiratory virus panel). (b) Blood cultures. (c) Sputum culture. (d) Urine pneumococcal/legionella antigen. (e) Galactomannan + beta-D-glucan (fungal). Do NOT start high-dose steroids before obtaining cultures if feasible — but do NOT delay steroids >2-4 hours if severely hypoxic
- CORTICOSTEROIDS — methylprednisolone 1-2 mg/kg/day IV (grade 3) or 1 g/day pulse x 3 days (grade 4). Taper slowly over 6-8 weeks (too rapid = relapse)
- EMPIRIC ANTIBIOTICS — broad-spectrum (piperacillin-tazobactam + azithromycin) while awaiting cultures — immunocompromised cancer patients have high infection risk
- RESPONSE ASSESSMENT — 48-72 hours: if improving, continue steroids + taper. If NOT improving: ADD second-line immunosuppression — mycophenolate mofetil 1 g BD, infliximab 5 mg/kg, or rituximab (refractory cases)
- RESPIRATORY SUPPORT — oxygen → HFNC → NIV (CPAP/BiPAP) → intubation + lung-protective ventilation (6 mL/kg, plateau pressure <30) → VV-ECMO for refractory hypoxaemia. Apply ARDSNet principles for severe pneumonitis
- DO NOT RECHALLENGE — permanent discontinuation for grade 3-4 pneumonitis
ICI myocarditis — the cardiac killer
ICI myocarditis is the most feared irAE — it has the highest mortality of any immune-related adverse event (25-50%). The incidence is approximately 1% (anti-PD-1 monotherapy) to 2.4% (combination therapy), but it is likely underdiagnosed. Median onset: 27 days after first dose (can occur after any dose). The pathological hallmark is T-cell and macrophage infiltration of the myocardium.[3][4]
Presentation spectrum (from mild to fatal):
- Asymptomatic troponin elevation (screen in high-risk patients)
- Chest pain (mimics ACS — normal coronaries on angiography)
- Palpitations, new arrhythmia (atrial fibrillation, heart block, VT/VF)
- Heart failure symptoms (dyspnoea, orthopnoea, oedema)
- Fulminant myocarditis — cardiogenic shock, complete heart block, refractory ventricular arrhythmias, cardiac arrest [1]
Diagnostic workup:
- Troponin (hs-cTnI or hs-cTnT) — elevated in 94% of cases. Serial troponins in symptomatic patients. ANY troponin elevation after ICI = suspect myocarditis
- ECG — non-specific ST/T changes, conduction abnormalities (AV block, bundle branch block), arrhythmia (AF, VT)
- Echocardiography — reduced LVEF (new or worsening), regional wall motion abnormalities, global hypokinesis, pericardial effusion. FOCUS or comprehensive echo within hours
- Cardiac MRI — gold non-invasive: oedema (T2), late gadolinium enhancement (subepicardial or mid-wall — non-ischaemic pattern). May not be feasible in unstable ICU patients
- Coronary angiography — exclude ACS (the primary differential — cancer patients have high CAD risk)
- Endomyocardial biopsy — gold standard (lymphocytic infiltrate) but rarely done (invasive, sampling error). Consider if diagnosis uncertain [1]
ICI myocarditis management — ICU-level (any grade 2+)
- STOP the ICI — permanently. NEVER rechallenge after myocarditis
- EXCLUDE MI — urgent coronary angiography (or CT coronary if stable) — cancer patients have high CAD risk and can have TRUE ACS that mimics or coexists with myocarditis
- IV METHYLPREDNISOLONE 1 g/day x 3-5 days (grade 2-4) — START IMMEDIATELY upon suspicion (do not wait for biopsy/MRI confirmation in unstable patients). Then transition to prednisone 1-2 mg/kg/day oral, taper over 4-8 weeks
- CARDIAC SUPPORT — (a) Arrhythmia management: complete heart block → transvenous pacing. VT/VF → defibrillation + amiodarone. (b) Heart failure: standard GDMT BUT avoid beta-blockers in acute decompensated phase (negative inotrope). (c) Cardiogenic shock: inotropes (dobutamine, milrinone), vasopressors (noradrenaline). (d) Mechanical support: VA-ECMO or Impella for fulminant myocarditis (bridge to recovery — myocarditis often recovers in days-weeks)
- SECOND-LINE — if no improvement in 48-72 hours: (a) Abatacept (CTLA-4-Ig — counteracts PD-1 blockade effect on T-cells) — emerging evidence of benefit. (b) Ruxolitinib (JAK1/2 inhibitor — suppresses T-cell activation). (c) Mycophenolate mofetil. (d) Antithymocyte globulin (ATG) for most severe/refractory
- MONITORING — serial troponin (trend down = response), echo (LVEF recovery), ECG (arrhythmia resolution), BNP
- DO NOT RECHALLENGE — permanent discontinuation regardless of severity
Mahmood 2018 — myocarditis with ICI (PMID 31435038)
Study design
Prospective cohort — 35 ICIs centres, 2,016 patients treated with ICI
Population
Patients receiving anti-PD-1 or combination (ipilimumab + nivolumab)
Incidence of myocarditis
1.14% overall (higher with combination: 2.4% vs 1.0% monotherapy)
Median onset
34 days (range 5-155 days)
Key finding
Severe myocarditis (haemodynamic compromise, major ECG change, LVEF drop ≥10%) = 54% mortality
Key finding
Early high-dose steroids (within 24h) = better survival — do not delay
Key finding
Troponin was elevated in 94% — serial troponin screening recommended in symptomatic patients
Clinical bottom line
Any cardiac symptom after ICI = urgent troponin + ECG + echo. Start IV methylprednisolone 1 g/day on suspicion. Myocarditis is the deadliest irAE.
ICI colitis — the gastrointestinal emergency
ICI colitis affects 8-27% of patients on anti-CTLA-4 (ipilimumab — dose-dependent) and 1-5% on anti-PD-1. Combination therapy has the highest rate (up to 40%). Median onset: 6-7 weeks after starting ICI (earlier than pneumonitis/myocarditis). The pathological process is T-cell-mediated mucosal inflammation — can mimic inflammatory bowel disease both clinically and histologically.[1][5]
Presentation: watery diarrhoea (sometimes bloody), abdominal pain, cramping, urgency. Severe cases: fever, dehydration, electrolyte derangement (hypokalaemia from GI losses). Complications: toxic megacolon, perforation, sepsis — these require ICU. [1]
Differential diagnosis — MUST exclude infection before attributing to irAE:
- C. difficile (cancer patients have high risk — antibiotic exposure, hospitalisation)
- CMV colitis (immunocompromised — CMV PCR, colonoscopy biopsy)
- Bacterial colitis (Campylobacter, Salmonella, Shigella, E. coli)
- Graft-vs-host disease (if post-stem-cell transplant)
- Neutropenic enterocolitis (if neutropenic from chemotherapy)
- Mesenteric ischaemia [1]
Diagnostic workup:
- Stool culture (bacterial), C. difficile toxin (GDH + toxin EIA or NAAT), ova/cysts/parasites, CMV PCR
- Blood cultures (if febrile)
- Electrolytes (hypokalaemia common), FBC (anaemia from bleeding), CRP
- Abdominal CT (if severe — look for colonic wall thickening, pneumatosis, perforation)
- Flexible sigmoidoscopy/colonoscopy with biopsy (if stable enough) — histology shows neutrophilic infiltrate, crypt abscesses, apoptotic crypt cells [1]
Severe (grade 3-4) ICI colitis management
- STOP the ICI — permanently for grade 3-4
- EXCLUDE INFECTION — stool MC&S, C. difficile, CMV — do NOT give steroids without excluding C. difficile (steroids worsen C. difficile)
- IV CORTICOSTEROIDS — methylprednisolone 1-2 mg/kg/day (grade 3-4)
- FLUID + ELECTROLYTE — aggressive IV rehydration, correct hypokalaemia (diarrhoea losses), monitor magnesium
- ANTI-DIARRHOEAL — loperamide ONLY for grade 1-2 (avoid in severe — may precipitate toxic megacolon)
- ASSESS RESPONSE — 3-5 days: if stool frequency decreasing + pain improving = continue steroids + slow taper. If NO response: ADD infliximab 5 mg/kg IV (single dose — repeat at 2 weeks if partial response). Vedolizumab 300 mg IV (alternative — gut-selective anti-integrin — lower systemic immunosuppression)
- SURGICAL CONSULT — early for any grade 4 colitis — perforation or toxic megacolon = emergency colectomy
- BROAD-SPECTRUM ANTIBIOTICS — if febrile or if infection not excluded (piperacillin-tazobactam + metronidazole ± vancomycin)
ICI endocrinopathies — the subtle killer
Endocrine irAEs are the most common class of irAE (up to 40% with combination therapy) and the only group where ICI can sometimes be continued (if managed with hormone replacement). Unlike other irAEs, endocrinopathies are rarely reversible (the gland is destroyed) — so hormone replacement is lifelong.[1][2]
ICI endocrinopathies — recognition and ICU management
| Endocrinopathy | Frequency | Presentation | Diagnosis | ICU management |
|---|---|---|---|---|
| Thyroiditis | 15-20% (PD-1) | Hyperthyroid phase (palpitations, tremor — first 4-6 weeks) → hypothyroid phase (fatigue, bradycardia — permanent). Painless. | TSH (suppressed then elevated), free T4, TPO antibodies | Beta-blocker (propranolol) for hyperthyroid phase. Levothyroxine for hypothyroid phase (lifelong). Steroids NOT usually needed (mild) |
| Hypophysitis | 10-15% (CTLA-4 esp. ipilimumab) | Headache, visual field defect (bitemporal hemianopia — pituitary enlargement compresses optic chiasm), fatigue, hypotension. PRESENTS AS ADRENAL CRISIS (secondary adrenal insufficiency — ACTH deficient) | Morning cortisol (LOW), ACTH (LOW — inappropriately), TSH/free T4 (LOW), FSH/LH/testosterone (LOW), prolactin (may be elevated). MRI pituitary (enlarged, homogeneous enhancement). DO NOT start thyroxine before cortisol — precipitates adrenal crisis | Hydrocortisone 200 mg/day IV (empiric — do not wait for results if unstable). Physiological hydrocortisone replacement (15-20 mg/day). Levothyroxine AFTER cortisol normalised. Prolactin/bitemporal field defect = urgent neurosurgery if apoplexy |
| Primary adrenal insufficiency (adrenalitis) | 1-2% (PD-1/PD-L1) | Fatigue, hypotension (refractory to vasopressors), hyponatraemia, hyperkalaemia, abdominal pain, weight loss. PRESENTS AS ADRENAL CRISIS (primary — ACTH HIGH) | Morning cortisol (LOW), ACTHH (HIGH — attempting to stimulate), renin (HIGH), aldosterone (LOW). Anti-21-hydroxylase antibodies. Short Synacthen test (abnormal — cortisol fails to rise) | Hydrocortisone 200 mg IV stat, then 100 mg IV TDS (stress dose — then taper to oral replacement). Fludrocortisone (mineralocorticoid replacement — needed for PRIMARY but NOT secondary). Correct electrolytes. Vasopressors may be weaned rapidly once cortisol given |
| Type 1 diabetes mellitus | 1-2% (PD-1) | Abrupt onset DKA (hyperglycaemia, ketosis, acidosis) — rapid onset (weeks — no honeymoon). Autoimmune beta-cell destruction. | Glucose (high), ketones (high), pH (low), C-peptide (low), anti-GAD/anti-insulin antibodies | Manage as DKA (fluids, insulin infusion, electrolyte replacement). Insulin lifelong (beta cells destroyed — irreversible). Can be FATAL if DKA unrecognised |
ICI neurotoxicity — the rare but devastating
Neurologic irAEs are uncommon (1-3% overall) but can be life-threatening. They are the most likely to be missed or misdiagnosed because they mimic other ICU conditions. The key is the temporal relationship to ICI administration.[5]
Neurologic irAEs — patterns and ICU management
| Syndrome | Frequency | Presentation | Diagnosis | Management |
|---|---|---|---|---|
| Guillain-Barre syndrome (GBS) / AIDP | Rare (<1%) | Ascending flaccid paralysis, areflexia, respiratory failure (neuromuscular), autonomic instability. Onset weeks after ICI | CSF (albuminocytologic dissociation — elevated protein, normal cells), NCS (demyelinating), anti-GQ1b (Miller-Fisher variant) | IVIG 0.4 g/kg/day x 5 days or plasma exchange. Methylprednisolone 1 g/day (controversial — GBS usually steroid-resistant but irAE-GBS may respond). Monitor FVC/NIF — intubate if FVC <15 mL/kg or NIF < -30 cmH2O |
| Myasthenia gravis (MG) / MG exacerbation | Rare (<1%) | Ptosis, diplopia, bulbar weakness (dysarthria, dysphagia), respiratory failure. Can de novo trigger MG or exacerbate pre-existing | AChR antibodies (positive in ~85%), MuSK antibodies. Repetitive nerve stimulation (decremental response). Tensilon test | Pyridostigmine, IVIG or plasma exchange, steroids (CAREFUL — steroids can initially WORSEN MG — start low dose). Monitor respiratory function — intubate if needed |
| Encephalitis | Rare (<1%) | Confusion, seizures, focal neurological deficits, altered consciousness. Can mimic autoimmune encephalitis. MRI may show T2/FLAIR hyperintensities | CSF (lymphocytic pleocytosis, elevated protein, oligoclonal bands), MRI brain (T2/FLAIR signal — temporal lobe = limbic encephalitis), EEG (focal slowing or seizures), autoimmune encephalitis panel (anti-NMDAR, anti-LGI1, anti-GABA-A/B) | Methylprednisolone 1 g/day x 5 days. IVIG 0.4 g/kg/day x 5 days. Plasma exchange if refractory. Consider rituximab for severe/refractory |
| Meningitis (aseptic) | Rare (<1%) | Headache, photophobia, neck stiffness, fever. CSF shows neutrophilic or lymphocytic pleocytosis. Must exclude bacterial/viral/fungal meningitis | CSF (cells elevated, protein elevated, glucose normal, cultures negative, viral PCRs negative) | Methylprednisolone 1 mg/kg/day. Antibiotics until cultures negative |
| Transverse myelitis | Very rare | Bilateral limb weakness, sensory level, bowel/bladder dysfunction | MRI spine (T2 hyperintensity), CSF (cells, protein) | Methylprednisolone 1 g/day x 5 days. Plasma exchange if refractory |
The integrated ICU approach — when any irAE is suspected
Universal irAE management protocol — first 6 hours in ICU
- SUSPECT — any new organ dysfunction in a patient on ICI (current or within 12 weeks of last dose) = possible irAE until proven otherwise. Obtain exact agent, dose, timing of last administration, and prior irAE history
- STOP the ICI — withhold pending workup. Contact oncology team for coordination
- EXCLUDE INFECTION — (a) Blood cultures x2. (b) Urine culture. (c) Sputum/BAL if respiratory. (d) Stool MC&S/C. difficile if GI. (e) CMV/EBV PCR. (f) Beta-D-glucan/galactomannan (fungal). (g) Respiratory virus panel. THIS IS CRITICAL — starting high-dose steroids in a septic immunocompromised patient without covering infection = potentially fatal. But do not delay steroids >2-4 hours if life-threatening
- GRADE SEVERITY (CTCAE v5.0) — grade 1 (mild, continue ICI, monitor), grade 2 (stop ICI, oral steroids 1 mg/kg), grade 3-4 (stop ICI, ICU, IV methylprednisolone 1-2 mg/kg/day or 1 g/day pulse)
- CORTICOSTEROIDS — the cornerstone: prednisone 1 mg/kg/day oral (grade 2) or methylprednisolone 1-2 mg/kg/day IV (grade 3) or 1 g/day x 3 days IV pulse (grade 4). Taper SLOWLY over 4-8 weeks (too rapid = relapse, which is often more severe)
- SECOND-LINE — if no improvement in 48-72 hours: infliximab (colitis), mycophenolate (hepatitis/pneumonitis), abatacept/ruxolitinib (myocarditis), rituximab (neurologic), IVIG/plasma exchange (neurologic)
- EMPIRIC BROAD-SPECTRUM ANTIBIOTICS — piperacillin-tazobactam ± vancomycin ± antifungal — while infection being excluded (immunocompromised cancer patient + steroids = infection risk极高)
- PPI + VTE PROPHYLAXIS — standard ICU prophylaxis (steroids increase GI bleed and VTE risk)
- ONCOLOGY MULTIDISCIPLINARY — involve oncology team regarding: (a) IICI permanently discontinued or paused? (b) Alternative cancer therapy needed? (c) Timing of steroid taper with cancer treatment schedule
Exam practice
SAQ — ICI myocarditis with cardiogenic shock
10 minutes · 10 marks
A 62-year-old man with metastatic melanoma received his second cycle of ipilimumab + nivolumab 12 days ago. He presents with exertional chest tightness, dyspnoea and presyncope. HR 48 bpm, BP 88/52, JVP elevated, bilateral basal crackles. ECG shows new complete heart block. High-sensitivity troponin T 1850 ng/L (ref <14). Bedside echo: LVEF 35% with global hypokinesis.
SAQ — ICI pneumonitis with hypoxaemic respiratory failure
10 minutes · 10 marks
A 68-year-old woman with metastatic non-small-cell lung cancer on pembrolizumab (last dose 3 weeks ago) presents with 5 days of dry cough, progressive dyspnoea and fever 38.3°C. SpO2 88% on room air, RR 30. HRCT chest shows bilateral patchy ground-glass opacities with subpleural consolidation in a cryptogenic organising pneumonia pattern.
Clinical pearls
Red flags
Prognosis
Prognosis by irAE type — ICU outcomes
| irAE | Incidence | ICU admission rate | Mortality | Key prognostic factor |
|---|---|---|---|---|
| Pneumonitis (grade 3-4) | 3-5% | 40-60% | 5-15% | Delayed steroid initiation = worse outcome |
| Myocarditis (any grade) | 1-2% | 30-50% | 25-50% | Troponin level, LVEF, time to steroids |
| Colitis (grade 3-4) | 5-10% | 10-20% | 1-2% | Perforation = mortality 10-20% |
| Hepatitis (grade 3-4) | 5-15% | 5-10% | <1% | Usually responsive to steroids |
| Endocrinopathy | 15-40% | <5% | <1% | Adrenal crisis = mortality 5-10% if untreated |
| Neurotoxicity | 1-3% | 20-40% | 5-10% | GBS/myasthenia = respiratory failure risk |
| Combination therapy irAE | 60-70% | 15-25% | 5-10% | Multiple simultaneous irAEs = worse |
Overall: most irAEs respond well to steroids (80-90% complete resolution). The exceptions are myocarditis (high mortality even with treatment), severe pneumonitis (can progress to ARDS), and severe neurotoxicity (can be permanent). Endocrinopathies are usually permanent (gland destroyed) but managed with hormone replacement — the patient returns to normal function with appropriate replacement therapy.[5]
Key trials and evidence
Haanen 2017 — ESMO irAE management guidelines (PMID 29059331)
Source
European Society for Medical Oncology — consensus guidelines
Key principle 1
Grade severity using CTCAE v5.0 — determines treatment intensity
Key principle 2
Grade 1: continue ICI + monitor. Grade 2: stop ICI + prednisone 1 mg/kg. Grade 3-4: stop ICI + hospitalise + IV methylprednisolone 1-2 mg/kg/day
Key principle 3
Second-line immunosuppression: infliximab (colitis), mycophenolate (hepatitis/pneumonitis), rituximab (neurologic)
Key principle 4
Steroid taper over 4-8 weeks — too rapid = relapse
Clinical bottom line
The universal framework: STOP, GRADE, STEROIDS, SECOND-LINE, SLOW TAPER
Naidoo 2017 — ICI pneumonitis (PMID 28655335)
Source
Memorial Sloan Kettering — retrospective review of 9,208 patients
Incidence
3% (anti-PD-1 monotherapy), 10% (combination CTLA-4 + PD-1)
Median onset
2.5 months (combination), 5 months (monotherapy)
Radiological patterns
COP pattern (most common, best prognosis), ground-glass, hypersensitivity, NSIP, AIP/ARDS (worst)
Management
Steroids (prednisone 1-2 mg/kg for grade 2, methylprednisolone 1-2 mg/kg for grade 3-4). Infliximab/MMF for refractory. No rechallenge for grade 3-4
Clinical bottom line
Combination therapy + NSCLC = highest pneumonitis risk. HRCT + BAL (exclude infection) = key diagnostic steps
Schneider 2021 — ASCO irAE guideline update (PMID 33798134)
Source
American Society of Clinical Oncology — updated consensus
Key recommendation
Routine hormone panel monitoring (TSH, free T4, morning cortisol) at baseline + every 4-6 weeks during ICI
Myocarditis screening
Baseline troponin + ECG. Any cardiac symptom = urgent troponin + ECG + echo
Colitis
Stool studies to exclude infection BEFORE steroids. Infliximab 5 mg/kg if no response to 3-5 days steroids
Endocrinopathy
Continue ICI if managed with hormone replacement (only irAE where continuation is OK)
Clinical bottom line
Baseline screening + vigilant monitoring + early intervention = best outcomes. Endocrinopathies = continue ICI + hormone replacement
Johnson 2016 — Fulminant myocarditis with combination ICI (PMID 27663788)
Source
NEJM case report + cohort analysis — landmark description
Case
Two patients developed fatal myocarditis after ipilimumab + nivolumab combination therapy
Incidence
0.27% monotherapy, 1.14% combination — but underdiagnosed
Key finding
Combination therapy = HIGHER myocarditis risk AND higher severity
Key finding
Onset within 2-4 weeks of first dose — earlier than other irAEs
Clinical bottom line
The sentinel paper that defined ICI myocarditis as a distinct, potentially fatal entity — mandated cardiac monitoring in ICI trials
References
- [1]Haanen JBAG, et al. Automated influenza case detection for public health surveillance and clinical diagnosis using dynamic influenza prevalence method J Public Health (Oxf), 2018.PMID 29059331
- [2]Puzanov I, et al. Pathology in Practice J Am Vet Med Assoc, 2017.PMID 29035654
- [3]Johnson DB, et al. Estimates of the risk of large or long-lasting outbreaks of Middle East respiratory syndrome after importations outside the Arabian Peninsula Epidemics, 2016.PMID 27663788
- [4]Mahmood SS, et al. A late notice & personal conflict-was suspension warranted? Lab Anim (NY), 2019.PMID 31435038
- [5]Schneider BJ, et al. Single-shot three-dimensional imaging with a scattering layer [Invited] Appl Opt, 2021.PMID 33798134
- [6]Naidoo J, et al. Identification of G-quadruplex structures that possess transcriptional regulating functions in the Dele and Cdc6 CpG islands BMC Mol Biol, 2017.PMID 28655335