What are the side effects of Kadcyla (ado‑trastuzumab emtansine)?

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Last updated: September 21, 2026 • View editorial policy

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Side Effects of Kadcyla (Ado-Trastuzumab Emtansine)

The most common side effects of Kadcyla (occurring in ≥25% of patients) are fatigue, nausea, musculoskeletal pain, hemorrhage, thrombocytopenia, headache, increased transaminases, and constipation 1.

Most Frequent Adverse Reactions

Based on the FDA label and clinical trial data from the EMILIA trial in metastatic breast cancer:

Very Common Side Effects (>25%)

  • Fatigue (36% all grades, 2.5% grade 3+)
  • Nausea (40% all grades, 0.8% grade 3+)
  • Musculoskeletal pain (36% all grades, 1.8% grade 3+)
  • Hemorrhage/bleeding (32% all grades, 1.8% grade 3+)
  • Thrombocytopenia (31% all grades, 15% grade 3+)
  • Increased liver transaminases (29% all grades, 8% grade 3+)
  • Headache (28% all grades, 0.8% grade 3+)
  • Constipation (27% all grades, 0.4% grade 3+) 1

Common Side Effects (10-25%)

  • Peripheral neuropathy (21% all grades, 2.2% grade 3+)
  • Epistaxis/nosebleeds (23% all grades, 0.2% grade 3+)
  • Diarrhea (24% all grades, 1.6% grade 3+)
  • Vomiting (19% all grades, 0.8% grade 3+)
  • Pyrexia/fever (19% all grades, 0.2% grade 3+)
  • Arthralgia (19% all grades, 0.6% grade 3+)
  • Abdominal pain (19% all grades, 0.8% grade 3+)
  • Asthenia (18% all grades, 0.4% grade 3+)
  • Cough (18% all grades, 0.2% grade 3+)
  • Anemia (14% all grades, 4.1% grade 3+)
  • Stomatitis (14% all grades, 0.2% grade 3+)
  • Myalgia (14% all grades, 0.6% grade 3+)
  • Dry mouth (17% all grades, 0% grade 3+)
  • Dyspnea (12% all grades, 0.8% grade 3+)
  • Rash (12% all grades, 0% grade 3+)
  • Insomnia (12% all grades, 0.4% grade 3+)
  • Hypokalemia (10% all grades, 2.7% grade 3+)
  • Dizziness (10% all grades, 0.4% grade 3+) 1

Serious and Life-Threatening Toxicities

Hepatotoxicity

Increased liver enzymes are common (29% all grades, 8% grade 3+) and represent one of the most frequent reasons for dose reduction or discontinuation 1. Severe hepatotoxicity including nodular regenerative hyperplasia and portal hypertension has been reported 2.

Cardiotoxicity

Left ventricular dysfunction can occur, though the rate is lower than with trastuzumab plus anthracyclines. Cardiac dysfunction ranged from 7-34% in adjuvant trials, with heart failure rates between 0-4% 3. Trastuzumab-containing agents (including T-DM1) show relative risks of 5.1 for cardiac dysfunction and 1.8 for heart failure 3.

Thrombocytopenia

Thrombocytopenia is the most common severe hematologic toxicity (31% all grades, 15% grade 3+) and a leading cause of dose reduction 1. Platelet counts require close monitoring throughout treatment.

Pulmonary Toxicity

Pneumonitis and interstitial lung disease have been reported. When combined with radiation therapy, there is concern for increased pneumonitis risk, though rates remain <1% for grade 3+ radiation-related pneumonitis 4.

Hemorrhage

Bleeding events occur in approximately 32% of patients (1.8% grade 3+), with epistaxis being the most common manifestation 1. Rare cases of hereditary hemorrhagic telangiectasia-like symptoms with mucocutaneous and liver telangiectasias have been reported 5.

Peripheral Neuropathy

Occurs in 21% of patients (2.2% grade 3+) and is one of the most frequent reasons for dose reduction 1.

Rare but Serious Complications

Hepatopulmonary Syndrome

A case series identified hepatopulmonary syndrome in patients receiving >50 doses of T-DM1, characterized by hypoxemia, portal hypertension, and intrapulmonary shunting. This typically presents with dyspnea and hypoxia on exertion, and may improve with drug discontinuation 2.

Infusion-Related Reactions

While T-DM1 is an antibody-drug conjugate containing trastuzumab, infusion reactions are less common than with standard trastuzumab (which has 20-40% incidence on first infusion, <1% severe) 6.

Treatment Discontinuation and Dose Modifications

In the EMILIA trial:

  • 7% discontinued due to adverse reactions (most commonly thrombocytopenia and increased transaminases)
  • 16% required dose reductions (most commonly for thrombocytopenia, increased transaminases, and peripheral neuropathy)
  • 24% experienced dose delays (most commonly for neutropenia, thrombocytopenia, leukopenia, fatigue, increased transaminases, and pyrexia) 1

Critical Monitoring Considerations

Monitor liver function tests and platelet counts before each dose. Cardiac function should be assessed at baseline and periodically during treatment, particularly in patients with prior anthracycline exposure or pre-existing cardiac conditions 7.

Watch for new dyspnea or hypoxia in patients on long-term therapy (>50 doses), as this may indicate hepatopulmonary syndrome requiring immediate evaluation 2.

References

4
Research

Safety profile of trastuzumab-emtansine (T-DM1) with concurrent radiation therapy: A systematic review and meta-analysis.

Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology, 2023

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.