Cetuximab

Mechanism of action

◎Epidermal growth factor receptor (EGFR), extracellular domain IIICetuximab

ⓘ The crystal shows the EGFR extracellular region with the cetuximab Fab bound to domain III, where it covers the site used by EGF.

Cetuximab is a chimeric mouse–human IgG1 antibody against domain III of the EGFR extracellular region. It blocks the binding of EGF and other ligands, prevents receptor dimerisation and switches off the growth and survival signals of the receptor; it can also trigger antibody-dependent cellular cytotoxicity. Tumours with KRAS mutations signal downstream of the receptor and do not benefit, so RAS status is tested in colorectal cancer.

1. Binds EGFR extracellular domain III
2. Ligand binding and dimerisation are blocked
3. Growth and survival signals stop; ADCC added
4. No benefit if KRAS is mutated (signal is downstream)

Indications

• Metastatic colorectal cancer that is KRAS (RAS) wild-type and expresses EGFR, alone or with irinotecan-based chemotherapy. Colorectal cancer →
• Head and neck squamous cell carcinoma: with radiotherapy for locally advanced disease, with platinum chemotherapy, or alone after platinum failure. Head and neck squamous cell carcinoma (oral cavity and oropharynx, HPV) →

Adverse effects

Common

• Acne-like (acneiform) rash in most patients
• Itching, dry skin, nail changes
• Headache
• Diarrhoea
• Low magnesium

Contraindications

• Previous severe infusion reaction to cetuximab
• Colorectal cancer with a RAS mutation (no benefit)
• Caution: coronary disease, heart failure, arrhythmia or low electrolytes

Key interactions

Radiotherapy (with or without platinum) in head and neck cancer

Higher risk of cardiopulmonary arrest; electrolytes and heart status are watched.

What is monitored

• Vital signs during and for at least one hour after each infusion
• Magnesium, potassium and calcium during and after treatment
• Skin and nails
• Cough or breathlessness (lung disease)
• RAS testing before use in colorectal cancer

Administration and safety

• Intravenous infusion only, never as a push or bolus; the first infusion is longer than the following ones.
• Ask about red-meat allergy and tick bites before the first dose: they predict severe reactions.
• Observe the patient for at least one hour after the infusion, with anaphylaxis drugs at hand.
• Look-alike names: cetuximab is checked against other -mab antibodies (e.g. panitumumab, bevacizumab).

Pregnancy and breastfeeding

May harm the fetus; a pregnancy test is done before starting and pregnancy is avoided during treatment and for months after; breastfeeding is avoided.

Nursing care

• Vital signs before, during and after the infusion; stop it and call for help if wheeze, hoarseness, facial swelling or hypotension appear.
• Check magnesium and potassium results and ask about cramps or palpitations.
• Skin care: gentle cleansing, moisturiser and sun protection for the rash.
• Teaching: report new cough or breathlessness and severe rash; contraception during and after treatment.

Pharmacokinetics

Absorption

Intravenous infusion; the first infusion runs longer than the following ones.

Distribution

Distribution close to the blood volume.

Elimination

Non-linear: partly removed by binding to EGFR (target-mediated clearance).

Half-life

About five days.

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Connections

← Back to the class: Antineoplastic monoclonal antibodies

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Cetuximab Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2021); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.