What is the mechanism of action, approved indication, common adverse effects, and their management for amivantamab?

Amivantamab: Mechanism, Indications, Adverse Effects, and Management

Amivantamab is a bispecific antibody targeting both EGFR and MET receptors that disrupts oncogenic signaling through ligand-binding blockade, receptor degradation, and immune-mediated tumor cell destruction via antibody-dependent cellular cytotoxicity (ADCC) and trogocytosis. 1

Mechanism of Action

Amivantamab binds to the extracellular domains of both EGFR and MET receptors, employing multiple mechanisms:

• Direct pathway disruption: Blocks ligand binding and promotes receptor degradation in EGFR exon 19 deletions, exon 21 L858R substitutions, and exon 20 insertions 1
• Immune engagement: Recruits natural killer cells and macrophages to destroy tumor cells through ADCC and trogocytosis mechanisms 1
• Dual targeting advantage: Simultaneously inhibits both EGFR and MET pathways, which is particularly relevant since MET amplification is a common resistance mechanism to EGFR inhibitors 2

The low-fucose formulation enhances immune effector function, distinguishing it from traditional tyrosine kinase inhibitors that cannot overcome the steric hindrance created by exon 20 insertions 2, 3.

FDA-Approved Indications

EGFR Exon 20 Insertions

• Second-line or later: Monotherapy for patients who have progressed after platinum-based chemotherapy 4, 5
• First-line: In combination with carboplatin-pemetrexed 5

EGFR Exon 19 Deletions or Exon 21 L858R Substitutions

• First-line: In combination with lazertinib 4
• Second-line: In combination with carboplatin-pemetrexed for patients who have progressed on osimertinib or other EGFR TKIs 4

The 2025 ASCO guidelines provide moderate-to-strong recommendations for amivantamab use in these settings, particularly emphasizing its role after osimertinib progression. 4

Common Adverse Effects

Infusion-Related Reactions (IRRs)

• Incidence: 64% (Grade ≥3: 3.1%) 1
• Timing: Predominantly during first infusion cycle 6
• Manifestations: Fever, chills, dyspnea, flushing, hypotension
• Severity: Most are mild-to-moderate; anaphylaxis is rare 1

Cutaneous Toxicities (EGFR-mediated)

• Rash: 80% of patients (acneiform pattern) 1, 6
• Paronychia: 50% (Grade ≥3: 3.1%) - nail fold inflammation and infection 1
• Pruritus: 18% 1
• Dry skin: 14% 1
• Other: Scalp abrasions (71%), skin fissures (57%), hair growth changes (hypertrichosis/hirsutism in 50-80%) 7

Venous Thromboembolism (VTE)

• Incidence: 19% (hemorrhage) 1
• Critical concern: Occurs even with prophylactic anticoagulation 6
• Mechanism: Likely multifactorial involving EGFR/MET pathway effects on coagulation

Peripheral Edema (MET-mediated)

• Incidence: 27% (Grade ≥3: 0.8%) 1
• Mechanism: MET inhibition affects fluid homeostasis and vascular permeability 8

Gastrointestinal Effects

• Diarrhea: 16% (Grade ≥3: 3.1%) - primarily EGFR-mediated 1
• Stomatitis: 26% (Grade ≥3: 0.8%) 1
• Nausea: 36% 1

Pulmonary Toxicity

• Interstitial lung disease/pneumonitis: <10% but potentially severe 1, 6
• Dyspnea: 37% (Grade ≥3: 2.3%) 1

Laboratory Abnormalities

• Hypoalbuminemia: 79% (Grade 3-4: 8%) 1
• Hyperglycemia: 56% (Grade 3-4: 4%) 1
• Lymphopenia: 36% (Grade 3-4: 8%) 1

Management Strategies

Infusion-Related Reactions

Prophylaxis (mandatory before each infusion):

• Antihistamines (diphenhydramine or equivalent)
• Antipyretics (acetaminophen)
• Corticosteroids (dexamethasone or methylprednisolone) 8

During infusion:

• First infusion: Administer over 5 hours with reduced rate for first 2 hours 1
• Subsequent infusions: Can reduce to 2 hours if first infusion tolerated 1
• Monitor vital signs every 30 minutes during infusion and 1 hour post-infusion 8

Grade 1-2 reactions:

• Interrupt infusion
• Administer additional antihistamines and corticosteroids
• Resume at 50% rate once symptoms resolve 8

Grade 3-4 reactions:

• Immediately discontinue infusion
• Administer epinephrine, IV fluids, oxygen as needed
• Permanently discontinue amivantamab 1, 8

Cutaneous Toxicities

Prophylactic approach (start 14 days before treatment):

• Oral tetracycline (doxycycline 100 mg twice daily or minocycline 100 mg daily) 7
• Topical corticosteroids (hydrocortisone 1-2.5% for face, higher potency for body)
• Intensive moisturization (fragrance-free, twice daily minimum)
• Sun protection (SPF 30+, physical blockers preferred) 8, 7

Rash management:

• Grade 1: Continue prophylaxis, increase topical steroid potency
• Grade 2: Add oral antibiotics if not already on prophylaxis, consider topical clindamycin
• Grade 3: Hold amivantamab until Grade ≤1, add oral prednisone 0.5 mg/kg if severe, dermatology consultation 8
• Dose modification: Reduce dose or permanently discontinue for recurrent Grade 3 1

Paronychia management:

• Prevention: Avoid tight shoes, keep nails short and clean, avoid manicures/pedicures 7
• Grade 1-2: Topical antibiotics (mupirocin), silver nitrate for granulation tissue, protective padding
• Grade 3: Oral antibiotics (cephalexin or fluoroquinolone), hold amivantamab, surgical debridement if needed 8

Diarrhea

Grade 1-2:

• Loperamide 4 mg initially, then 2 mg after each loose stool (max 16 mg/day)
• Aggressive hydration and electrolyte replacement
• Dietary modifications (BRAT diet, avoid dairy/high-fiber) 8

Grade 3-4:

• Hold amivantamab until Grade ≤1
• Consider octreotide if refractory to loperamide
• Rule out infectious causes (C. difficile, particularly if on antibiotics)
• IV hydration if dehydrated 8

Venous Thromboembolism

Prophylaxis considerations:

• Risk assessment using validated tools (Khorana score)
• Consider prophylactic anticoagulation in high-risk patients, though breakthrough events still occur 6
• Patient education on VTE symptoms (leg swelling, chest pain, dyspnea)

Treatment:

• DVT/PE: Therapeutic anticoagulation (LMWH or DOAC per institutional guidelines)
• Continue amivantamab with close monitoring
• Consider IVC filter if anticoagulation contraindicated
• Massive PE: Fibrinolytics or thrombectomy 6

Peripheral Edema

Grade 1-2:

• Leg elevation, compression stockings
• Sodium restriction
• Diuretics (furosemide 20-40 mg daily) if symptomatic 8

Grade 3:

• Hold amivantamab until Grade ≤1
• Increase diuretic dose
• Rule out cardiac or renal causes
• Consider dose reduction upon resumption 8

Interstitial Lung Disease/Pneumonitis

Any grade pneumonitis:

• Immediately discontinue amivantamab permanently 1
• High-dose corticosteroids (prednisone 1-2 mg/kg or equivalent)
• Pulmonary consultation
• Rule out infection with bronchoscopy if clinically indicated
• Taper steroids over 4-6 weeks once improved 8

Stomatitis

Grade 1-2:

• Bland oral rinses (saline or sodium bicarbonate)
• Topical anesthetics (viscous lidocaine, "magic mouthwash")
• Avoid alcohol-based mouthwashes and spicy/acidic foods 8

Grade 3:

• Hold amivantamab until Grade ≤1
• Consider systemic corticosteroids if severe
• Nutritional support (soft diet, nutritional supplements)

Dose Modifications

Weight-tiered dosing:

• <80 kg: 1,050 mg IV
• ≥80 kg: 1,400 mg IV 1, 9

Schedule:

• Weeks 1-4: Weekly
• Week 5 onward: Every 2 weeks (monotherapy) or every 3 weeks (with chemotherapy) 1, 9

Dose reductions for toxicity:

• First reduction: 840 mg (<80 kg) or 1,120 mg (≥80 kg)
• Second reduction: 700 mg (<80 kg) or 840 mg (≥80 kg)
• Permanently discontinue if unable to tolerate second dose reduction 1

Critical Pitfalls to Avoid

1. Inadequate IRR prophylaxis: Always premedicate; most reactions occur during first infusion 8
2. Delayed cutaneous toxicity management: Start prophylactic antibiotics and moisturizers 14 days before treatment, not after rash develops 7
3. Underestimating VTE risk: Maintain high clinical suspicion even with prophylactic anticoagulation 6
4. Missing pneumonitis: Any new respiratory symptoms require immediate evaluation; permanently discontinue if confirmed 1
5. Ignoring psychological impact: Cutaneous toxicities significantly affect quality of life; provide psychological support and realistic expectations 7

Special Populations

No dose adjustment needed for:

• Age (21-88 years studied)
• Mild-moderate renal impairment (eGFR 30-89 mL/min)
• Mild hepatic impairment
• Race or ethnicity 1

Pregnancy/Lactation:

• Contraindicated; verify pregnancy status before initiation
• Use effective contraception during treatment and 3 months after
• Do not breastfeed during treatment and 3 months after 1