Kadcyla (Trastuzumab Emtansine)

Kadcyla is used in the management of HER2‑positive breast cancer, targeting the HER2 signaling pathway.

• HER2‑positive metastatic breast cancer: improves progression‑free and overall survival in patients with advanced disease.
• HER2‑positive early breast cancer (adjuvant setting): reduces the risk of disease recurrence after surgery and standard therapy.
• HER2‑positive locally advanced breast cancer: provides disease control when surgery is not immediately feasible.

• Trastuzumab emtansine combines a humanized monoclonal antibody that binds the extracellular domain of the HER2 receptor with the cytotoxic agent DM1, a maytansine derivative. After intravenous infusion, the antibody directs the conjugate to HER2‑overexpressing tumor cells, where the complex is internalized. Inside the cell, DM1 is released, binds tubulin, and inhibits microtubule assembly, leading to cell‑cycle arrest and apoptosis.

Kadcyla may cause a range of adverse reactions, varying in frequency and severity.

Common Side Effects

• Fatigue: feeling of tiredness or lack of energy.
• Nausea: sensation of needing to vomit, often mild.
• Thrombocytopenia: reduced platelet count that may increase bleeding risk.
• Elevated liver enzymes: increased ALT or AST indicating hepatic stress.

Serious or Rare Side Effects

• Cardiac toxicity: decrease in left ventricular ejection fraction or heart failure.
• Interstitial lung disease: inflammation of lung tissue that can be life‑threatening.
• Severe infusion reactions: anaphylaxis, hypotension, or bronchospasm during administration.

Before initiating Kadcyla therapy, several precautions should be observed to minimize risks.

• Cardiac monitoring: perform baseline and periodic left ventricular ejection fraction assessments.
• Liver function assessment: check transaminases before each treatment cycle.
• Platelet count monitoring: evaluate for thrombocytopenia and adjust dosing if needed.
• Hypersensitivity avoidance: do not administer to patients with known allergy to trastuzumab or DM1.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Kadcyla can interact with other medicines, affecting safety or efficacy.

Major Interactions (Avoid)

• Concomitant trastuzumab: increased risk of cardiac dysfunction.
• Anthracycline chemotherapy: additive cardiotoxicity when given together.
• Live vaccines: may reduce vaccine effectiveness and increase infection risk.
• Strong CYP3A4 inhibitors (e.g., ketoconazole): may raise DM1 exposure and toxicity.

Moderate Interactions (Monitor Closely)

• Anticoagulants: heightened bleeding risk due to thrombocytopenia.
• Hormonal therapies (e.g., tamoxifen): potential additive hepatic effects.
• CYP3A4 inducers (e.g., rifampin): may lower DM1 levels and reduce efficacy.