Residency · Residency · Internal Medicine
Immune Checkpoint Inhibitor Toxicity
Introduction
Immune checkpoint inhibitors (ICIs) have revolutionized oncology by unleashing anti-tumor immune responses. However, this immune activation can lead to immune-related adverse events (irAEs) affecting virtually any organ system. Internists and hospitalists increasingly manage these toxicities as ICI use expands across cancer types. Early recognition and prompt immunosuppressive therapy are critical to preventing morbidity and mortality.
Checkpoint Inhibitor Classes
- Anti-CTLA-4: ipilimumab; blocks the inhibitory CTLA-4 receptor on T-cells
- Anti-PD-1: nivolumab, pembrolizumab, cemiplimab; block PD-1 receptor on T-cells
- Anti-PD-L1: atezolizumab, durvalumab, avelumab; block PD-L1 ligand on tumor cells
- Combination therapy (anti-CTLA-4 + anti-PD-1) has the highest efficacy but also the highest toxicity rate (55-60% grade 3-4 irAEs)
- irAEs can occur at any time during therapy and even months after discontinuation
General Principles of irAE Management
| Grade | Severity | ICI Action | Immunosuppression |
|---|---|---|---|
| 1 | Mild | Continue ICI | Close monitoring; symptomatic treatment |
| 2 | Moderate | Hold ICI | Prednisone 0.5-1 mg/kg |
| 3 | Severe | Hold ICI | Prednisone 1-2 mg/kg (or IV methylprednisolone) |
| 4 | Life-threatening | Permanently discontinue | High-dose IV steroids; add infliximab/MMF if refractory |
- Grading: CTCAE (Common Terminology Criteria for Adverse Events) grades 1-4
- Grade 1: continue ICI with close monitoring
- Grade 2: hold ICI; consider moderate-dose corticosteroids (0.5-1 mg/kg prednisone)
- Grade 3: hold ICI; high-dose corticosteroids (1-2 mg/kg prednisone or methylprednisolone)
- Grade 4: permanently discontinue ICI; high-dose IV corticosteroids; consider additional immunosuppression
- Taper steroids slowly over 4-6 weeks minimum to prevent relapse
- If no response to steroids within 48-72 hours, escalate to infliximab, mycophenolate, or other immunosuppressants
Organ-Specific Toxicities
| Organ System | Frequency | Most Common Manifestation | Steroid-Refractory Agent |
|---|---|---|---|
| Dermatologic | 30-50% | Maculopapular rash | Dermatology referral |
| Gastrointestinal | 20-35% | Colitis/diarrhea | Infliximab or vedolizumab |
| Endocrine | 10-20% | Thyroiditis, hypophysitis | Hormone replacement (not immunosuppression) |
| Hepatic | 5-15% | Immune hepatitis | Mycophenolate (avoid infliximab) |
| Pneumonitis | 3-10% | Cough, dyspnea, GGOs | Infliximab or mycophenolate |
| Renal | 2-5% | Acute interstitial nephritis | Mycophenolate |
| Cardiac | 1-2% | Myocarditis (25-50% mortality) | Abatacept, ATG |
| Neurologic | 1-5% | Myasthenia gravis, GBS | IVIG, plasmapheresis |
Dermatologic (Most Common, 30-50%)
- Maculopapular rash: most common irAE; usually mild; topical steroids for grade 1-2
- Pruritus: antihistamines and topical steroids
- Severe reactions: SJS/TEN, bullous pemphigoid; permanently discontinue ICI; dermatology consultation
Gastrointestinal (20-35%)
- Colitis: diarrhea, abdominal pain, hematochezia; more common with anti-CTLA-4
- Evaluate with stool studies (C. difficile, cultures), CT abdomen, and colonoscopy if grade 2+
- Management: high-dose steroids; infliximab (5 mg/kg) if steroid-refractory; vedolizumab as alternative
- Avoid opioids and anti-motility agents until infection is excluded
Hepatic (5-15%)
- Immune hepatitis: elevated AST/ALT, often asymptomatic
- Rule out viral hepatitis, drug-induced liver injury, and metastatic disease
- Management: hold ICI for grade 2+; steroids for grade 3+; mycophenolate for steroid-refractory cases
- Avoid infliximab for hepatotoxicity (hepatotoxic itself)
Endocrine (10-20%)
- Thyroiditis: may present as initial thyrotoxicosis followed by hypothyroidism; check TSH, free T4
- Hypophysitis: headache, fatigue, hypopituitarism; more common with anti-CTLA-4; MRI shows pituitary enlargement
- Primary adrenal insufficiency: rare but life-threatening; morning cortisol, ACTH stimulation test
- Type 1 diabetes (fulminant): can present as DKA; check C-peptide, GAD antibodies
- Hormone replacement is typically lifelong; steroids do not reverse endocrine destruction
Pneumonitis (3-10%)
- Cough, dyspnea, hypoxia; more common with anti-PD-1/PD-L1
- CT chest shows ground-glass opacities, organizing pneumonia, or interstitial patterns
- Rule out infection (sputum cultures, BAL if needed) and disease progression
- Management: hold ICI; high-dose steroids; infliximab or mycophenolate if refractory
Cardiac (1-2%, but High Mortality)
- Myocarditis: most feared cardiac irAE; mortality 25-50%
- Presents with chest pain, dyspnea, arrhythmias, heart failure, cardiogenic shock
- Elevated troponin, BNP; ECG changes; cardiac MRI showing edema; endomyocardial biopsy is definitive
- Management: high-dose IV methylprednisolone (1 g/day x 3-5 days); early cardiology consultation
- Often co-occurs with myositis and myasthenia gravis
Neurologic (1-5%)
- Myasthenia gravis: fatigable weakness, ptosis, dysphagia, respiratory failure
- Guillain-Barre syndrome: ascending weakness, areflexia
- Encephalitis: confusion, seizures, personality changes
- Peripheral neuropathy: sensory or motor; may be asymmetric
- Neurology consultation mandatory; treatment includes steroids, IVIG, or plasmapheresis
Renal (2-5%)
- Acute interstitial nephritis: most common; rising creatinine, sterile pyuria, eosinophiluria
- Rule out other causes: obstruction, dehydration, nephrotoxins
- Renal biopsy may be needed for diagnosis
- Management: hold ICI; steroids for grade 2+
Monitoring and Surveillance
- Baseline labs before each cycle: CBC, CMP, TSH, LFTs, urinalysis
- Educate patients to report new symptoms promptly; irAEs can present insidiously
- Monitor for irAEs for at least 12 months after discontinuation
- Multidisciplinary collaboration between oncology, affected subspecialties, and primary care is essential
Key Clinical Pearls
- irAEs can affect any organ system and can present weeks to months after ICI discontinuation.
- Corticosteroids are the cornerstone of irAE management; taper slowly over at least 4-6 weeks.
- Myocarditis is rare but carries the highest mortality of all irAEs; maintain a high index of suspicion.
- Endocrine irAEs (thyroiditis, hypophysitis) require lifelong hormone replacement; steroids do not reverse them.
- When in doubt, hold the checkpoint inhibitor and start steroids; early treatment improves outcomes.
References
- Brahmer JR, Abu-Sbeih H, Ascierto PA, et al. Society for Immunotherapy of Cancer (SITC) Clinical Practice Guideline on Immune Checkpoint Inhibitor-Related Adverse Events. Journal for ImmunoTherapy of Cancer. 2021;9(6):e002435.
- Postow MA, Sidlow R, Hellmann MD. Immune-Related Adverse Events Associated with Immune Checkpoint Blockade. New England Journal of Medicine. 2018;378(2):158-168.
- Schneider BJ, Naidoo J, Santomasso BD, et al. Management of Immune-Related Adverse Events in Patients Treated with Immune Checkpoint Inhibitor Therapy: ASCO Guideline Update. Journal of Clinical Oncology. 2021;39(36):4073-4126.
- Moslehi JJ, Salem JE, Sosman JA, et al. Increased Reporting of Fatal Immune Checkpoint Inhibitor-Associated Myocarditis. The Lancet. 2018;391(10124):933.