Kadcyla (ado-trastuzumab emtansine, or T-DM1) is an antibody-drug conjugate used to treat HER2-positive breast cancer. It combines two medicines linked together:

• Trastuzumab: a monoclonal antibody that specifically targets the HER2 protein on cancer cells
• Emtansine (DM1): a potent chemotherapy agent that kills cells by disrupting their internal structure

T-DM1 acts like a guided missile. The trastuzumab part finds cancer cells that overexpress HER2, binds to them, and delivers chemotherapy directly inside the cell, minimising impact on surrounding healthy tissue.

Kadcyla is used for HER2-positive locally advanced or metastatic breast cancer after prior trastuzumab and taxane treatment, and as adjuvant treatment after surgery when residual disease was found.

Kadcyla is given as an intravenous (IV) infusion in a hospital or infusion centre by trained medical staff. You will not administer this medicine at home.

It is given once every three weeks. The first infusion takes 90 minutes, and if well tolerated, subsequent infusions may be given over 30 minutes.

You will be monitored during and after each infusion for any reactions.

Your infusions are scheduled by your oncology team. Contact them if you need to reschedule an appointment.

In a clinical setting, any dosing error is managed immediately by medical staff.

Storage is handled by the treating clinic. Kadcyla vials are stored in a refrigerator between 2°C and 8°C.

Side effects are common and some can be serious.

Very common side effects:

• Fatigue
• Nausea
• Low platelets (thrombocytopenia): increases risk of bleeding and bruising. Platelet counts are checked before each cycle
• Low white blood cells (neutropenia)
• Liver enzyme elevations
• Peripheral neuropathy: tingling, numbness, or pain in the hands and feet
  

Serious side effects:

• Cardiac toxicity: Kadcyla can reduce heart pumping function. Heart function is checked by echocardiogram regularly
• Interstitial lung disease: new breathlessness or cough should be reported promptly
• Infusion reactions: fever, chills, shortness of breath, or low blood pressure during or after infusion
• Hepatotoxicity: liver problems including rare but serious liver injury

Blood tests and heart function checks are part of routine monitoring during treatment.

• Strong CYP3A4 inhibitors (ketoconazole, clarithromycin): may increase emtansine exposure. Avoid if possible
• Other cardiotoxic medicines: combined cardiac toxicity risk

Tell your oncologist about all medicines you are taking.

How is Kadcyla different from Herceptin (trastuzumab)?

Herceptin is trastuzumab alone. Kadcyla is trastuzumab chemically linked to a chemotherapy drug. While Herceptin works by blocking HER2 signalling, Kadcyla also delivers chemotherapy directly inside HER2-positive cancer cells, making it more potent against certain HER2-positive cancers after prior treatment.

What is thrombocytopenia and why should I watch for it?

Thrombocytopenia means low platelets, the blood cells that help clotting. When platelets are low, you bruise more easily and bleed longer from cuts. Tell your doctor about any unusual bruising, nosebleeds, blood in urine or stools, or very heavy periods. Your platelet count will be checked before every infusion, and dose delays may be needed if counts fall too low.

Ace provides accurate and independent information medically reviewed on prescription medications. This material is provided for educational purposes only and is not intended for medical advice, diagnosis or treatment.