Herzuma (Trastuzumab)

Herzuma is prescribed for patients whose tumors overexpress the human epidermal growth factor receptor 2 (HER2). The drug is used in both early and advanced disease settings across several cancer types.

• HER2‑positive metastatic breast cancer, in combination with chemotherapy.
• HER2‑positive early breast cancer, as adjuvant or neoadjuvant therapy.
• HER2‑positive gastric or gastro‑esophageal junction adenocarcinoma, together with chemotherapy.
• HER2‑positive locally advanced or unresectable breast cancer, when surgery is not feasible.
• HER2‑positive disease in patients who have completed prior trastuzumab‑containing regimens, as per clinical guidance.

• Trastuzumab binds with high affinity to the extracellular domain IV of the HER2 receptor on tumor cells. This binding blocks ligand‑independent HER2 dimerization, suppresses downstream signaling pathways such as PI3K/AKT and MAPK, and promotes antibody‑dependent cellular cytotoxicity (ADCC) by recruiting immune effector cells. The combined inhibition of proliferative signals and immune‑mediated tumor cell killing underlies its antineoplastic activity overall and contributes to clinical benefit.

Adverse reactions to Herzuma vary in frequency and severity, reflecting its immunologic and vascular effects.

Common

• Infusion‑related reactions such as fever, chills, flushing, or hypotension.
• Nausea, vomiting, or mild gastrointestinal upset including abdominal discomfort.
• Fatigue, headache, dizziness, or mild skin rash at the injection site.

Serious

• Cardiac dysfunction, including reduced left ventricular ejection fraction or congestive heart failure.
• Severe hypersensitivity or anaphylactic reactions, potentially requiring emergency treatment.
• Thromboembolic events such as deep‑vein thrombosis, pulmonary embolism, or arterial occlusion.

Before initiating Herzuma, clinicians should evaluate several patient‑specific factors to minimize risk and ensure appropriate monitoring.

• Assess baseline cardiac function with echocardiography or MUGA scan, and repeat periodically.
• Review history of hypersensitivity reactions to monoclonal antibodies or trastuzumab‑containing products.
• Evaluate hepatic and renal function, adjusting treatment if significant impairment is present.
• Monitor for signs of infusion‑related reactions during and after each administration.
• Use caution in patients with uncontrolled hypertension or active infections.
• Discuss contraception and potential fetal risks, as safety in pregnancy has not been established.

Herzuma may interact with other medicines that affect cardiac function, immune response, or drug clearance.

Avoid

• Concurrent use of anthracyclines (e.g., doxorubicin) due to increased risk of cardiotoxicity.
• Live vaccines during treatment, because immune suppression may reduce vaccine efficacy and increase infection risk.

Use with caution

• Chemotherapeutic agents that also cause myelosuppression, requiring close blood count monitoring.
• Medications that prolong QT interval, as cardiac monitoring is already indicated.
• Hormonal therapies (e.g., tamoxifen) that may have additive cardiac effects.