Kadcyla (T-DM1): What to Expect, Side Effects, and More
Kadcyla (chemical name: T-DM1 or ado-trastuzumab emtansine) is a type of medicine called an antibody-drug conjugate (ADC) used to treat:
HER2-positive metastatic breast cancer that has previously been treated with Herceptin (chemical name: trastuzumab) and taxane chemotherapy
Early-stage HER2-positive breast cancer after surgery, if residual disease was found after neoadjuvant (before surgery) treatment with Herceptin and taxane chemotherapy
Kadcyla is a combination of Herceptin and the chemotherapy medicine emtansine. The emtansine is attached (conjugated) to the Herceptin.
See Kadcyla prescribing information.
How Kadcyla works
Breast cancer cells that are HER2-positive make too many HER2 receptors. These receptors receive signals that stimulate the cell to grow and multiply.
Herceptin works by attaching to the HER2 receptor and blocking it from receiving growth signals.
Emtansine, like some other chemotherapy medicines, disrupts the way cells grow.
Emtansine isn’t a targeted medicine, which means it can affect healthy cells as well as cancer cells. Emtansine is never given alone to treat any type of cancer — it’s too toxic. Kadcyla was designed to deliver emtansine to cancer cells in a targeted way by attaching emtansine to Herceptin. Herceptin then carries emtansine to the HER2-positive cancer cells. This way, the emtansine is less toxic to healthy cells and more effective in stopping cancer cell growth.
What to expect during Kadcyla treatment
Kadcyla is given intravenously, which means the medicine is delivered directly into your bloodstream through an IV or port. Kadcyla is usually given as an infusion every 3 weeks.
People diagnosed with metastatic disease get Kadcyla every 3 weeks unless the cancer grows or unacceptable side effects develop. People diagnosed with early-stage disease get Kadcyla every 3 weeks for a total of 14 cycles or until unacceptable side effects develop.
Kadcyla side effects
Like almost all breast cancer medicines, Kadcyla can cause side effects, some of them severe.
The most common side effects of Kadcyla are:
low blood platelet count
low potassium levels
Kadcyla can also cause other serious side effects. While these serious side effects are rare (about 1% to 2% of people treated with Kadcyla will experience them), it’s important to know what to watch for:
Heart problems: Kadcyla may cause serious heart problems, including some that don’t have symptoms, such as reduced heart function, and some that do have symptoms, such as congestive heart failure. Your health care provider will assess your heart function both before and during your treatment. Symptoms to watch for include swelling of the ankles or legs, shortness of breath, cough, or weight gain of more than 5 pounds in less than 24 hours.
Lung problems: Kadcyla may cause inflammation of the lungs, which can be life-threatening. Symptoms include trouble breathing, cough, tiredness, and fluid in the lungs.
Liver problems: Kadcyla may cause severe liver problems, including liver failure. Symptoms include swelling or pain in the abdomen; a yellow tint in the eyes or skin (jaundice); swollen legs, feet, or ankles.
If you’re pregnant or planning to get pregnant, you should not be given Kadcyla. Kadcyla can cause embryo death and birth defects. You must use effective birth control while being treated. You shouldn’t breastfeed while taking Kadcyla or for several months after you stop taking the medicine.
Real patient reviews
Members of our community discuss their experiences with Kadcyla in the community forum. Here are some of their comments. Remember, it's essential to talk to your doctor about any side effects you're having and ask about ways to manage them.
“I had my first Kadcyla infusion (with decadron and zofran IV) three weeks ago and experienced the following side effects: 3 days after - thigh soreness, fatigue; 4 - 6 days after - terrible headache for 3 days with strong nausea; 7+ days after - constipation and feeling like my food was not fully digesting, increased reflux, difficulty sleeping, and fatigue.” — sarawil
“I did 14 rounds of Kadcyla from October '22 through July '23. Days 4-6 were when I felt the worst. I had GI issues for the entire time, particularly queasiness, indigestion, reflux, and constipation. I took 2 stool softeners daily. Fatigue was an issue, but I don't know if it was the Kadcyla or continued effects of the chemo/surgery that preceded it.” — maggiehopley
“I was taking Kadcyla well for the first 5 and 6 sessions out of 14, but then slowly started getting terrible muscle cramps and dry eyes [as well as] other common side effects. I just had 9th session last week and now I feel like I'm beat.” —momofquackytoddler
Read more in our Kadcyla discussion forum.
Paying for Kadcyla
The cost of Kadcyla may vary. The price you’ll pay depends on the drug manufacturer, your health insurance provider and plan, where you live, and the pharmacy you use.
Note: Your insurance company may require you to get prior authorization before covering Kadcyla.
Learn more about financial assistance and medicine cost-lowering tips.
— Last updated on June 1, 2025 at 2:20 PM
