Kadcyla (Trastuzumab Emtansine)
Antibody-drug conjugate for HER2-positive breast cancer
Quick Facts About Kadcyla
Key Takeaways About Kadcyla
- Targeted cancer therapy: Kadcyla delivers chemotherapy directly into HER2-positive cancer cells, reducing damage to healthy tissue compared to conventional chemotherapy
- Not interchangeable: Kadcyla must not be confused with trastuzumab (Herceptin) or trastuzumab deruxtecan (Enhertu) – these are different medicines with different safety profiles
- Regular monitoring required: Liver function, platelet counts, and heart function must be checked before and during treatment
- Pregnancy warning: Kadcyla can cause serious harm to an unborn baby – effective contraception is essential during treatment and for 7 months after the last dose
- Infusion reactions possible: The first infusion takes 90 minutes with observation; subsequent infusions may be shortened to 30 minutes if well tolerated
What Is Kadcyla and What Is It Used For?
Kadcyla (trastuzumab emtansine) is an antibody-drug conjugate that combines a targeted antibody with a potent cytotoxic agent to treat HER2-positive breast cancer. It is approved for metastatic disease and as adjuvant therapy after surgery in patients who have previously received trastuzumab and a taxane.
Kadcyla belongs to a class of cancer medicines known as antibody-drug conjugates (ADCs). It is composed of two key components linked together: trastuzumab, a monoclonal antibody that selectively binds to the human epidermal growth factor receptor 2 (HER2), and DM1, a maytansinoid cytotoxic agent. These two components are connected via a stable thioether linker that keeps the drug intact while circulating in the bloodstream.
HER2 is a protein found on the surface of certain cancer cells. When present in abnormally high quantities (HER2-positive cancer), it drives uncontrolled cell growth. Trastuzumab recognizes and binds to HER2 on the surface of these cancer cells. Once bound, the entire Kadcyla molecule is internalized by the cancer cell. Inside the cell, DM1 is released, where it disrupts the cell's microtubule network, effectively preventing the cancer cell from dividing and ultimately causing it to die.
This targeted mechanism of action is what distinguishes Kadcyla from conventional chemotherapy. Rather than affecting all rapidly dividing cells throughout the body, Kadcyla delivers its cytotoxic payload specifically to HER2-overexpressing cancer cells. This targeted delivery aims to improve anticancer efficacy while reducing some of the systemic side effects associated with traditional chemotherapy regimens.
Approved Indications
Kadcyla is approved for the treatment of HER2-positive breast cancer in adults in two main clinical settings:
- Metastatic breast cancer: For patients whose cancer has spread to areas near the breast or to other parts of the body (metastasized), and who have previously received trastuzumab and a taxane chemotherapy agent, either separately or in combination.
- Adjuvant treatment: For patients with early-stage HER2-positive breast cancer who have residual invasive disease after neoadjuvant (pre-surgical) treatment with trastuzumab and a taxane. In this setting, Kadcyla is given after surgery to reduce the risk of cancer recurrence.
Before starting Kadcyla, your doctor will test your cancer cells to confirm they are HER2-positive. Only patients with confirmed HER2-overexpressing tumors are eligible for Kadcyla treatment. HER2 status is typically determined through immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH) testing.
What Should You Know Before Taking Kadcyla?
Before starting Kadcyla, inform your doctor about all medical conditions, particularly liver problems, heart conditions, and current medications. Kadcyla is contraindicated in patients with known hypersensitivity to trastuzumab emtansine or any of its excipients. It requires careful monitoring throughout treatment.
Contraindications
You must not receive Kadcyla if you are allergic (hypersensitive) to trastuzumab emtansine or any of the other ingredients in this medicine. The excipients include succinic acid, sodium hydroxide, sucrose, and polysorbat 20. If you have a known allergy to any of these components, inform your healthcare team before treatment begins.
Warnings and Precautions
Talk to your doctor or nurse before using Kadcyla if any of the following apply to you:
- You have had a serious infusion-related reaction to trastuzumab, characterized by symptoms such as flushing, chills, fever, shortness of breath, breathing difficulties, rapid heartbeat, or low blood pressure
- You are receiving treatment with blood-thinning medicines such as warfarin or heparin
- You have ever had problems with your liver – your doctor will order blood tests to check your liver function before and regularly during treatment
- Breathing problems: Shortness of breath (at rest or during activity) and cough, which may be signs of lung inflammation (pneumonitis) – a potentially life-threatening condition
- Liver problems: Yellowing of skin and eyes (jaundice), dark urine, nausea, or abdominal pain, which may indicate serious liver damage
- Heart problems: Shortness of breath at rest or during sleep, chest pain, swollen legs or arms, rapid or irregular heartbeat
- Infusion reactions: Flushing, shaking, fever, breathing difficulty, low blood pressure, rapid heartbeat, swelling of face or tongue during or after infusion
- Bleeding: Unexpected bruising, nosebleeds, bleeding gums, or any unusual bleeding, indicating low platelet counts
- Nerve damage: Tingling, pain, numbness, itching, or pins-and-needles sensation in hands and feet
Liver toxicity is one of the most important risks associated with Kadcyla. The medicine can cause inflammation or damage to liver cells, leading to elevated levels of liver enzymes in blood tests. In most cases, these elevations are mild and temporary. However, in rare cases, a condition called nodular regenerative hyperplasia (NRH) can develop, which changes the liver's structure and function. Over time, this can lead to symptoms such as abdominal swelling due to fluid accumulation or bleeding from altered blood vessels in the esophagus or rectum.
Cardiotoxicity is another significant concern. Kadcyla can weaken the heart muscle, reducing its ability to pump blood effectively. Your doctor will monitor your heart function using echocardiograms or MUGA scans before starting treatment and at regular intervals throughout therapy. Patients with pre-existing heart conditions may require more frequent monitoring.
Thrombocytopenia (low platelet count) is very common with Kadcyla treatment. Because platelets are essential for blood clotting, reduced platelet counts can lead to unexpected bruising or bleeding. Your doctor will regularly check your blood counts and may need to adjust your dose or delay treatment if platelet levels fall too low.
Pregnancy and Breastfeeding
Kadcyla is not recommended during pregnancy as it may cause harm to the developing baby. If you are pregnant, think you may be pregnant, or are planning to become pregnant, consult your doctor before receiving this medicine.
You must use effective contraception to avoid becoming pregnant during treatment with Kadcyla. Continue using contraception for 7 months after the last dose. Discuss the most appropriate contraceptive method with your doctor. Male patients or their female partners should also use effective contraception during this period.
You should not breastfeed during treatment with Kadcyla or for a period of 7 months after the last infusion. It is unknown whether the components of Kadcyla pass into breast milk. Speak with your doctor about the safest approach for feeding your baby during and after treatment.
Children and Adolescents
Kadcyla is not recommended for anyone under 18 years of age. This is because there is no information available about how the medicine works in this age group. Clinical trials have not been conducted in pediatric populations for this indication.
Driving and Operating Machinery
Kadcyla is not expected to affect your ability to drive or operate machinery under normal circumstances. However, if you experience infusion-related reactions (flushing, shaking, fever, breathing difficulties, low blood pressure, rapid heartbeat), blurred vision, fatigue, headache, or dizziness, you should not drive, cycle, or operate tools or machinery until these reactions have subsided.
How Does Kadcyla Interact with Other Drugs?
Kadcyla can interact with several medications, particularly strong CYP3A4 inhibitors, anticoagulants, and certain antifungal, antibiotic, and HIV medications. These interactions may increase the risk of side effects or alter the effectiveness of treatment. Always inform your healthcare team about all medications you are taking.
The DM1 component of Kadcyla is metabolized partly by the CYP3A4 enzyme system. Medications that strongly inhibit CYP3A4 can increase the concentration of DM1 in the body, potentially leading to increased toxicity. While formal drug interaction studies are limited, caution is advised when Kadcyla is co-administered with known CYP3A4 inhibitors.
Major Interactions
The following medications may have clinically significant interactions with Kadcyla and require careful monitoring or avoidance:
| Drug / Drug Class | Type of Interaction | Clinical Significance |
|---|---|---|
| Ketoconazole, Itraconazole, Voriconazole (antifungals) | Strong CYP3A4 inhibition – may increase DM1 levels | Avoid concomitant use if possible; monitor closely for increased toxicity |
| Clarithromycin, Telithromycin (antibiotics) | Strong CYP3A4 inhibition – may increase DM1 exposure | Consider alternative antibiotics; increased monitoring required |
| Atazanavir, Indinavir, Nelfinavir, Ritonavir, Saquinavir (HIV antivirals) | Strong CYP3A4 inhibition – may increase DM1 levels | Use with caution; discuss with HIV specialist and oncologist |
| Nefazodone (antidepressant) | Strong CYP3A4 inhibition | Avoid if possible; consider alternative antidepressant |
Minor Interactions
The following medications require awareness when used with Kadcyla:
| Drug / Drug Class | Type of Interaction | Clinical Advice |
|---|---|---|
| Warfarin (anticoagulant) | Increased bleeding risk due to thrombocytopenia | Monitor INR frequently; adjust warfarin dose as needed |
| Heparin (anticoagulant) | Increased bleeding risk due to thrombocytopenia | Use with caution; monitor platelet counts closely |
| Acetylsalicylic acid (Aspirin) | Increased bleeding risk due to antiplatelet effect | Weigh benefits vs. bleeding risk; monitor for signs of bleeding |
Always inform your doctor, nurse, or pharmacist about all medications you are currently taking, have recently taken, or plan to take. This includes prescription medicines, over-the-counter drugs, herbal supplements, and vitamins. Some interactions may not be immediately apparent and require clinical judgement to manage safely.
What Is the Correct Dosage of Kadcyla?
Kadcyla is administered at a dose of 3.6 mg per kilogram of body weight, given as an intravenous infusion every three weeks (21-day cycle). The first infusion lasts approximately 90 minutes; if well tolerated, subsequent infusions can be given over 30 minutes. Your doctor calculates your individual dose based on your weight.
Kadcyla is always administered by a doctor or nurse in a hospital or clinic setting. It is given as a drip into a vein (intravenous infusion) and must never be given as an intravenous push or bolus injection. The medicine requires preparation (reconstitution and dilution) by trained healthcare professionals before administration.
Adults
Standard Adult Dosage
Dose: 3.6 mg/kg body weight
Frequency: Every 3 weeks (21-day cycle)
Route: Intravenous infusion
First infusion: Administered over approximately 90 minutes. You will be observed by medical staff during the infusion and for at least 90 minutes afterward for any adverse reactions.
Subsequent infusions: If the first infusion is well tolerated, subsequent infusions may be given over approximately 30 minutes, with at least a 30-minute observation period afterward.
The total number of infusions you receive depends on how you respond to treatment and the indication being treated. For metastatic breast cancer, treatment typically continues as long as the cancer is responding and side effects remain manageable. For adjuvant treatment, the standard course is 14 cycles (approximately 10 months).
If you experience side effects, your doctor may decide to continue treatment at a lower dose, delay the next dose, or discontinue treatment entirely. Dose reductions follow a structured protocol: the first reduction is to 3.0 mg/kg, and the second reduction is to 2.4 mg/kg. If further dose reduction is needed below 2.4 mg/kg, treatment is typically discontinued.
Children
Kadcyla is not recommended for use in children and adolescents under 18 years of age. No clinical data are available in this population, and the safety and efficacy have not been established.
Elderly
No dose adjustment is required for elderly patients based on age alone. Clinical trial data included patients over 65 years, and no overall differences in safety or efficacy were observed compared to younger patients. However, elderly patients may be more susceptible to certain side effects, particularly cardiotoxicity and hepatotoxicity, and may require closer monitoring.
Missed Dose
If you miss or forget your appointment for Kadcyla treatment, schedule a new appointment as soon as possible. Do not wait until your next planned visit. Your doctor will determine when you should receive your next dose and will adjust the treatment schedule accordingly. The interval between doses should not be less than 21 days.
Overdose
Since Kadcyla is administered by healthcare professionals in a controlled clinical setting, overdose is unlikely. There is no known specific antidote for Kadcyla. In the event of overdose, the patient should be closely monitored and supportive care provided as clinically indicated. If you are concerned about the amount of medicine you have received, speak with your doctor or nurse immediately.
What Are the Side Effects of Kadcyla?
Like all medicines, Kadcyla can cause side effects, although not everyone gets them. The most common side effects include elevated liver enzymes, nausea, fatigue, thrombocytopenia (low platelets), musculoskeletal pain, and peripheral neuropathy. Some side effects can be serious and require immediate medical attention.
Side effects of Kadcyla are categorized below by how frequently they occur. Understanding the frequency of side effects can help you and your healthcare team monitor for potential problems and take action promptly when needed. Your doctor will regularly check your blood counts, liver function, and heart function throughout treatment.
Very Common Side Effects
May affect more than 1 in 10 patients
- Elevated liver enzymes (AST/ALT) in blood tests
- Thrombocytopenia (low platelets) – causing unexpected bruising or bleeding (e.g., nosebleeds)
- Peripheral neuropathy – tingling, pain, numbness, itching, pins-and-needles in hands and feet
- Decreased red blood cell count (anemia)
- Nausea and vomiting
- Diarrhea
- Dry mouth
- Urinary tract infection
- Constipation
- Abdominal pain
- Cough
- Shortness of breath
- Mouth inflammation (stomatitis)
- Difficulty sleeping (insomnia)
- Muscle or joint pain (musculoskeletal pain)
- Fever
- Headache
- Fatigue
- Weakness (asthenia)
Common Side Effects
May affect up to 1 in 10 patients
- Infusion-related reactions – flushing, shaking, fever, breathing difficulty, low blood pressure, rapid heartbeat (during or up to 24 hours after infusion)
- Heart problems – decreased left ventricular function, shortness of breath, chest pain, swollen ankles or arms
- Chills or flu-like symptoms
- Decreased potassium levels (hypokalemia)
- Skin rash
- Decreased white blood cell count (neutropenia)
- Dry eyes, watery eyes, or blurred vision
- Eye redness or infection
- Indigestion (dyspepsia)
- Swollen legs and/or arms (peripheral edema)
- Gum bleeding
- Increased blood pressure (hypertension)
- Dizziness
- Taste disturbances (dysgeusia)
- Itching (pruritus)
- Memory difficulties
- Hair loss (alopecia)
- Hand-foot skin reaction (palmar-plantar erythrodysesthesia)
- Nail changes
Uncommon Side Effects
May affect up to 1 in 100 patients
- Pneumonitis (lung inflammation) – causing shortness of breath, dry cough, or coughing fits
- Allergic reactions – ranging from mild (itching, chest tightness) to severe (facial/tongue swelling, difficulty swallowing or breathing)
- Nodular regenerative hyperplasia (NRH) of the liver – a structural change that can affect liver function, causing abdominal swelling or gastrointestinal bleeding
- Injection site reactions – tenderness, redness, or swelling at the infusion site (if the solution leaks outside the vein)
Rare Side Effects
May affect up to 1 in 1,000 patients
- Severe liver damage with jaundice (yellowing of skin and whites of the eyes)
If Kadcyla infusion solution leaks out of the vein into the surrounding tissue (extravasation), you may develop pain, discoloration, blistering, and skin breakdown (necrosis) at the infusion site within days or weeks. Tell your doctor or nurse immediately if you feel burning, pain, or tenderness at the infusion site during the infusion.
If you experience any side effects after Kadcyla treatment has been discontinued, inform your doctor or nurse and let them know that you have been treated with Kadcyla, as some effects can appear or persist after treatment ends.
How Should You Store Kadcyla?
Kadcyla is stored and handled by healthcare professionals at the hospital or clinic. Unopened vials must be refrigerated at 2°C to 8°C and must not be frozen. Once reconstituted, the solution is stable for up to 24 hours at 2°C to 8°C.
As Kadcyla is administered in a clinical setting, you will not need to store the medicine at home. However, understanding the storage requirements ensures confidence in the quality of the medicine you receive:
- Unopened vials: Store in a refrigerator at 2°C to 8°C (36°F to 46°F). Do not freeze.
- Reconstituted solution: Stable for up to 24 hours at 2°C to 8°C. Must be discarded after this period.
- Diluted infusion solution: Should be administered immediately once prepared. If not used immediately, it can be stored for up to 24 hours at 2°C to 8°C. Do not freeze or shake.
- Shelf life: Do not use after the expiration date (EXP) printed on the carton and vial. The expiration date refers to the last day of the stated month.
Keep this medicine out of the sight and reach of children. Unused medicine should not be disposed of via household waste or wastewater. Healthcare facilities follow specific protocols for the safe disposal of cytotoxic medicines to protect the environment.
What Does Kadcyla Contain?
Kadcyla contains the active substance trastuzumab emtansine. It is available as 100 mg and 160 mg vials of white to slightly yellowish freeze-dried powder that is reconstituted with sterile water before administration.
Active Substance
The active substance is trastuzumab emtansine, an antibody-drug conjugate consisting of trastuzumab linked to DM1 (a maytansinoid cytotoxic agent) via a stable MCC (4-[N-maleimidomethyl] cyclohexane-1-carboxylate) linker.
- Kadcyla 100 mg vial: Contains 100 mg trastuzumab emtansine. After reconstitution with 5 mL sterile water for injection, each vial contains 5 mL of solution at a concentration of 20 mg/mL.
- Kadcyla 160 mg vial: Contains 160 mg trastuzumab emtansine. After reconstitution with 8 mL sterile water for injection, each vial contains 8 mL of solution at a concentration of 20 mg/mL.
Other Ingredients (Excipients)
- Succinic acid
- Sodium hydroxide
- Sucrose
- Polysorbat 20
This medicine contains less than 1 mmol sodium (23 mg) per dose, meaning it is essentially sodium-free. The 100 mg vial contains 1.1 mg polysorbat 20 (corresponding to 0.22 mg/mL), and the 160 mg vial contains 1.7 mg polysorbat 20 (corresponding to 0.21 mg/mL). Polysorbates can cause allergic reactions in some individuals. If you have known allergies, inform your doctor.
Appearance and Packaging
Kadcyla is a white to slightly yellowish freeze-dried (lyophilized) powder for concentrate for solution for infusion, supplied in glass vials. Each pack contains one single-use vial. The reconstituted solution should be clear to slightly opalescent, and colorless to slightly brownish. Do not use if the solution appears cloudy or discolored.
Kadcyla is manufactured by Roche Pharma AG, Emil-Barell-Strasse 1, 79639 Grenzach-Wyhlen, Germany. The marketing authorization holder is Roche Registration GmbH.
Kadcyla contains less than 1 mmol sodium (23 mg) per dose. This is considered essentially "sodium-free" and is generally not a concern for patients on sodium-restricted diets.
Frequently Asked Questions About Kadcyla
Kadcyla (trastuzumab emtansine) is used to treat HER2-positive breast cancer in adults. It is prescribed for metastatic breast cancer (cancer that has spread) and as adjuvant therapy after surgery in patients who have already received trastuzumab and a taxane chemotherapy. Kadcyla works as an antibody-drug conjugate, delivering a potent cytotoxic agent directly to HER2-overexpressing cancer cells while minimizing damage to healthy tissue.
The most common side effects (affecting more than 1 in 10 patients) include elevated liver enzymes, nausea, fatigue, thrombocytopenia (low platelet count leading to bruising or bleeding), musculoskeletal pain, headache, constipation, peripheral neuropathy (tingling or numbness in hands and feet), and anemia. Most of these side effects are manageable with dose modifications and supportive care. Your medical team will monitor you closely throughout treatment.
Kadcyla is given as an intravenous (IV) infusion every 3 weeks at a dose of 3.6 mg per kilogram of body weight. The first infusion takes approximately 90 minutes, followed by at least 90 minutes of observation. If well tolerated, subsequent infusions may be shortened to about 30 minutes with a 30-minute observation period. It is always administered by trained healthcare professionals in a hospital or clinic.
Yes, Kadcyla can affect heart muscle function (cardiotoxicity). This is monitored through regular echocardiograms or MUGA scans before and during treatment. Symptoms of heart problems may include shortness of breath (especially at rest or during sleep), chest pain, swelling in legs or arms, and rapid or irregular heartbeat. If you experience any of these symptoms, contact your medical team immediately. In some cases, treatment may need to be paused or discontinued.
No, Kadcyla and trastuzumab (Herceptin) are different medicines and must never be substituted for each other. While both contain trastuzumab and target HER2, Kadcyla is an antibody-drug conjugate that also carries a cytotoxic agent (DM1). This gives Kadcyla a dual mechanism of action: targeted HER2 binding plus intracellular delivery of chemotherapy. Similarly, Kadcyla should not be confused with trastuzumab deruxtecan (Enhertu), which is a different antibody-drug conjugate. Always verify which product is being administered.
Before starting Kadcyla, tell your doctor about: any liver problems or liver disease; heart conditions or history of heart failure; if you are taking blood-thinning medications (warfarin, heparin, aspirin); if you have had previous infusion-related reactions to trastuzumab; all other medications including antifungals (ketoconazole, itraconazole), antibiotics (clarithromycin), HIV medications, and antidepressants (nefazodone); if you are pregnant, planning to become pregnant, or breastfeeding. This information helps your doctor assess the risks and benefits of treatment for your individual situation.
References
- European Medicines Agency (EMA). Kadcyla (trastuzumab emtansine) – Summary of Product Characteristics. Last updated 2025. Available at: ema.europa.eu/en/medicines/human/EPAR/kadcyla
- U.S. Food and Drug Administration (FDA). KADCYLA (ado-trastuzumab emtansine) Prescribing Information. Genentech, Inc. Reference ID: 4756982.
- Verma S, Miles D, Gianni L, et al. Trastuzumab emtansine for HER2-positive advanced breast cancer. N Engl J Med. 2012;367(19):1783-1791. doi:10.1056/NEJMoa1209124
- von Minckwitz G, Huang CS, Mano MS, et al. Trastuzumab emtansine for residual invasive HER2-positive breast cancer (KATHERINE trial). N Engl J Med. 2019;380(7):617-628. doi:10.1056/NEJMoa1814017
- National Comprehensive Cancer Network (NCCN). Clinical Practice Guidelines in Oncology: Breast Cancer. Version 2.2025.
- Cardoso F, Paluch-Shimon S, Senkus E, et al. 5th ESO-ESMO international consensus guidelines for advanced breast cancer (ABC 5). Ann Oncol. 2020;31(12):1623-1649. doi:10.1016/j.annonc.2020.09.010
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List, 2023. Geneva: WHO; 2023.
- Dieras V, Miles D, Verma S, et al. Trastuzumab emtansine versus capecitabine plus lapatinib in patients with previously treated HER2-positive advanced breast cancer (EMILIA): a descriptive analysis of final overall survival results from a phase 3, randomised, open-label trial. Lancet Oncol. 2017;18(6):732-742. doi:10.1016/S1470-2045(17)30312-1
Editorial Team
iMedic Medical Editorial Team – this article was written and medically reviewed by our team of specialist physicians in oncology, pharmacology, and clinical medicine. All content follows international guidelines from the EMA, FDA, NCCN, and ESMO, and adheres to the GRADE evidence framework.
All medical information is reviewed by board-certified specialists with expertise in oncology and clinical pharmacology.
Evidence Level 1A based on systematic reviews, randomized controlled trials (EMILIA, KATHERINE), and international clinical guidelines.
No pharmaceutical company funding or advertising. Completely independent medical editorial content.
This article was last medically reviewed on and will be reviewed again within 12 months.