Results from the TH3RESA study show that Kadcyla (chemical name: T-DM1 or ado-trastuzumab emtansine), a targeted therapy medicine, improved overall survival in women diagnosed with metastatic, HER2-positive breast cancer that had stopped responding to Herceptin (chemical name: trastuzumab) and Tykerb (chemical name: lapatinib) compared to the women’s doctors’ treatment of choice.
The study, “Trastuzumab emtansine improves overall survival versus treatment of physician’s choice in patients with previously treated HER2-positive metastatic breast cancer: Final overall survival results from the phase 3 TH3RESA study,” (Abstract S5-05) was presented on Dec. 11, 2015 at the 2015 San Antonio Breast Cancer Symposium.
Kadcyla is a combination of Herceptin and the chemotherapy medicine emtansine. In Kadcyla, the emtansine is attached to the Herceptin. In earlier studies on Kadcyla, it was reported that the chemotherapy medicine maytansine was attached to Herceptin to form Kadcyla. Emtansine is a derivative of maytansine.
Kadcyla is approved by the U.S. Food and Drug Administration (FDA) to treat HER2-positive metastatic breast cancer that has previously been treated with Herceptin and a taxane chemotherapy.
Herceptin is approved by the FDA to treat advanced-stage, HER2-positive breast cancers and to lower the risk of recurrence of early-stage, HER2-positive breast cancer with a high risk of recurrence. HER2-positive breast cancers make too much of the HER2 protein. The HER2 protein sits on the surface of cancer cells and receives signals that tell the cancer to grow and spread. About one out of every four breast cancers is HER2-positive. Herceptin works by attaching to the HER2 protein 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.
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.
Metastatic breast cancer is breast cancer that has come back in a part of the body away from the breast, such as the bones, liver, or brain.
Overall survival is how long a woman lives, whether or not the cancer grows.
In the TH3RESA study, the researchers compared Kadcyla to a woman’s doctor’s choice of treatments for metastatic, HER2-positive breast cancer that had been previously treated with Herceptin, Tykerb, and a taxane chemotherapy to see which would offer more benefits.
Previous results from the TH3RESA study found that Kadcyla improved the time women diagnosed with metastatic, HER2-positive disease lived without the cancer growing (disease-free survival) compared to the doctor’s choice of treatment.
The results presented in San Antonio in 2015 looked at overall survival.
The TH3RESA study included 602 women diagnosed with metastatic, HER2-positive breast cancer that had been previously treated with a chemotherapy regimen that included a taxane and, after being diagnosed with metastatic disease, two or more regimens that included the targeted therapies Herceptin and Tykerb. Both Herceptin and Tykerb target the HER2 protein.
More than half the women received four or more earlier treatments.
The women were randomly assigned to get either:
- 3.6 mg of Kadcyla per kg of body weight every 3 weeks (404 women)
- treatment chosen by their doctor (198 women)
After about 2.5 years of follow-up, the results showed that overall survival was:
- 22.7 months for women treated with Kadcyla
- 15.8 months for women who got the treatment chosen by their doctor
Because the results were so positive, women who were receiving the treatment chosen by their doctor were allowed to switch to Kadcyla if they wanted to do so; nearly 45% decided to cross over to Kadcyla.
“Here we show that T-DM1 actually increased overall survival for heavily pretreated patients with HER2-positive, metastatic breast cancer. This is very important because several breast cancer therapies that increase progression-free survival do not in fact increase overall survival, and these patients urgently need new treatment options,” said Hans Wildiers, M.D., Ph.D., professor of medical oncology at KU Leuven in Belgium.
“The difference in overall survival was highly statistically significant,” he continued, “despite so many women crossing over [switching from their doctors’ treatment of choice to Kadcyla] and about 80% of the women receiving Herceptin before.”
Statistically significant means that the difference in overall survival was likely due to the difference in treatment and not just because of chance.
Dr. Wildiers also said that as of February 2015, 25% of the women in the study still had stable disease -- meaning the cancer had not grown since the study started in 2011.
Severe side effects are unfortunately common with many cancer treatments. About 40% of the women who got Kadcyla had severe side effects compared to 47.3% of the people who got their doctor’s choice of treatment.
“Not only did the population of patients assigned T-DM1 have increased median overall survival, they also had reduced incidence of grade 3 and higher adverse events,” said Dr. Wildiers. “The fact that these patients lived longer with less toxicity suggests that T-DM1 is a good treatment option even for patients who have received two or more HER2-targeted treatment regimens.”
If you’re being treated for metastatic HER2-positive breast cancer that has stopped responding to a targeted therapy regimen that included Herceptin and/or Tykerb, this study offers encouraging news. It’s a good idea to ask your doctor about this study and Kadcyla and whether it might be a good treatment option for you based on your unique situation.
For more information, visit the Breastcancer.org Kadcyla pages.
Editor's Note: On May 3, 2019, the FDA approved Kadcyla to treat early-stage HER2-positive breast cancer after surgery if residual disease was found after neoadjuvant treatment with taxane chemotherapy and Herceptin.
Read more Research News from the 2015 San Antonio Breast Cancer Symposium:
- Treating Residual Disease With Xeloda Improves Survival in Women With Early-Stage, HER2-Negative Disease
- Arimidex or Tamoxifen Reduce Recurrence Risk After DCIS Equally Well in Postmenopausal Women, Choice Depends on Age, Side Effects
- Study Suggests Premenopausal Women With Certain Type of Breast Cancer Don’t Benefit From Chemotherapy
- Lumpectomy Plus Radiation May Offer Survival Benefits for Early-Stage Disease
- Prolia Reduces Recurrence Risk of Hormone-Receptor-Positive Disease in Women Taking Aromatase Inhibitors
- Triple-Negative Disease May Have New Treatment Option