Study: Severe Side Effects Uncommon After Taking T-DM1

Breast Cancer News
December 15, 2014
Erin Rowley, Writer and Content Coordinator
Reviewed By: 
George W. Sledge, Jr., MD

After looking at information from seven studies involving T-DM1 (Kadcyla), researchers found that severe side effects were uncommon. If they did occur, they were usually manageable.

Background and Goals

T-DM1 is an antibody-drug conjugate, a treatment that pairs a chemotherapy medicine with a targeted therapy to get the chemotherapy directly to tumor cells. This causes fewer side effects than when the two medicines are given separately. In this case, the targeted therapy is trastuzumab (Herceptin). This medicine is used to treat HER2-positive breast cancer, which grows when breast cells have too many HER2 proteins.

T-DM1 was approved by the FDA for treatment of HER2-positive, metastatic breast cancer in 2013 after the EMILIA study showed it did a better job of lengthening life and stopping the cancer from growing than standard treatments.

The EMILIA study and other research involving T-DM1 has created a large pool of information about how people react to the medicine. These researchers used that data to look at the safety of T-DM1 on a large scale.


Researchers looked at side effect information from seven studies involving T-DM1. Those studies featured 884 people who took at least one dose of T-DM1.


This study found 17.2 percent of people needed their dose changed because of side effects and 7 percent stopped treatment because of side effects. The most common side effects of any severity level were:

  • Fatigue (46.4 percent)
  • Nausea (43 percent)
  • Low blood platelet count (32.2 percent)
  • Headache (29.4 percent)
  • Constipation (26.5 percent)

The most common grade 3, severe, or higher, side effect was low blood platelet count, seen in 11.9 percent of participants. This side effect shows up in lab readings and could cause bleeding problems such as nosebleeds, but overall it was unlikely to be noticed by participants.

Asians were more likely to have grade 3 or higher side effects, especially low blood platelet count. Those 65 and older were also slightly more likely to have grade 3 or higher side effects. Twelve side effect-related deaths were recorded, which is about 1.3 percent of participants in the study.

What This Means for You

If you have HER2-positive, metastatic breast cancer and are taking, or considering taking T-DM1, this study may make you feel hopeful, because your chance of severe side effects is low.

Though they are not likely, serious side effects are still possible with T-DM1. Your blood platelet count should be checked while on the medicine. Any blood thinner use should be watched closely, because it could increase your chance of severe bleeding.

Be open with your doctor about how you’re feeling and how the medicine is affecting your well-being. Report any side effects and remember to talk about any concerns you have.

T-DM1 is also being studied in early stage, HER2-positive breast cancer. If you’re interested in learning more about that research, visit and talk to your doctor.

Diéras, Véronique; Harbeck, Nadia; Budd, G. Thomas. Trastuzumab Emtansine in Human Epidermal Growth Factor Receptor 2–Positive Metastatic Breast Cancer: An Integrated Safety AnalysisJournal of Clinical Oncology. Published online ahead of print July 14, 2014; doi: 10.1200/JCO.2013.54.4999.

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