Herceptin (Trastuzumab)

Herceptin is indicated for several HER2‑positive malignancies, typically as part of combination regimens.

• HER2‑positive metastatic breast cancer, often combined with chemotherapy.
• HER2‑positive early breast cancer in the adjuvant setting, following surgery.
• HER2‑positive gastric or gastroesophageal junction adenocarcinoma, in combination with chemotherapy.
• HER2‑positive metastatic gastric cancer when other therapies are appropriate.
• Investigational use in other HER2‑expressing tumors under clinical study.

• Trastuzumab is a humanized IgG1 monoclonal antibody that binds with high affinity to the extracellular domain IV of the human epidermal growth factor receptor 2 (HER2). By occupying this site, it blocks ligand‑independent HER2 dimerization and downstream signaling through the PI3K/AKT and MAPK pathways. The bound antibody also recruits immune effector cells, leading to antibody‑dependent cellular cytotoxicity and tumor cell lysis.

Herceptin may cause a spectrum of adverse reactions, from mild infusion‑related symptoms to potentially life‑threatening events, and the frequency varies among patients.

Common

• Infusion‑related reactions such as fever, chills, nausea, flushing, or rigors.
• Fatigue, asthenia, or general weakness.
• Diarrhea, abdominal cramping, or mild gastrointestinal upset.
• Headache, dizziness, or transient visual disturbances.
• Mild rash, skin erythema, or pruritus; occasional transient elevation of liver enzymes.

Serious

• Cardiac dysfunction, including reduced left ventricular ejection fraction or congestive heart failure.
• Severe hypersensitivity reactions, including anaphylaxis and bronchospasm.
• Pulmonary toxicity such as interstitial pneumonitis or acute respiratory distress.

When prescribing Herceptin, clinicians should evaluate patient history and monitor specific clinical parameters to reduce risk of complications.

• Baseline and periodic assessment of cardiac function (e.g., echocardiogram or MUGA scan).
• Avoid use in patients with uncontrolled cardiac disease or recent myocardial infarction.
• Monitor for signs of infusion reactions; premedication with antihistamines and corticosteroids may be recommended.
• Assess liver function tests before each infusion and adjust if significant elevations occur.
• Use caution in pregnant or breastfeeding women; the drug may cross the placenta and its safety is not established.
• Evaluate for potential drug interactions, especially with cardiotoxic agents.

Herceptin can interact with other medicines, influencing its safety profile or therapeutic effectiveness.

Avoid

• Concurrent use with other HER2‑targeted monoclonal antibodies (e.g., pertuzumab) without appropriate clinical justification, due to overlapping toxicity.
• Co‑administration with cardiotoxic chemotherapeutics (e.g., anthracyclines) in the same cycle, which may increase cardiac risk.

Use with caution

• Concomitant use of live vaccines, as immune modulation may affect vaccine efficacy.
• Combination with drugs that prolong QT interval, requiring cardiac monitoring.
• Concurrent administration of strong CYP3A4 inducers or inhibitors is not expected to affect trastuzumab significantly, but clinical judgment is advised.