Early results from a very small, very early study suggests that some advanced-stage, HER2-positive breast cancers that have stopped responding to Herceptin (chemical name: trastuzumab) may respond to one of two experimental treatments:
- T-DM1, an experimental targeted therapy medicine that's a combination of Herceptin and the chemotherapy medicine maytansine; the maytansine is attached to the Herceptin, which doctors call "conjugated"
- T-DM1 and Omnitarg (chemical name: pertuzumab), another experimental targeted therapy
The results were presented at the 2010 American Society of Clinical Oncology (ASCO) annual meeting.
Herceptin is used to treat advanced-stage, HER2-positive breast cancer and to lower the risk of recurrence of early-stage, HER2-positive breast cancer with a high risk of recurrence. HER2-positive 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.
Maytansine (DM1), like some other chemotherapy medicines, disrupts the way cells grow. Maytansine on its own isn't considered a targeted therapy, which means it can affect healthy cells as well as cancer cells. T-DM1 was designed to deliver maytansine to cancer cells in a targeted way by attaching the maytansine to the Herceptin. Herceptin then carries the maytansine only to the cancer cells.
Like Herceptin, Omnitarg works by stopping the HER2 protein from telling cancer cells to grow.
In the on-going study, 43 women and one man diagnosed with advanced-stage, HER2-positive breast cancer that had stopped responding to Herceptin were treated with either T-DMI alone or T-DM1 with Omnitarg. These early results are from 28 women in the study.
Of those 28 women, 23 (82%) got some benefit from T-DM1 and Omnitarg:
- 10 women (35.7%) had a partial response (the cancer was weakened)
- 13 women (46.4%) had disease stabilization (the cancer stopped growing)
Four women had the cancer grow while being treated with T-DM1 and Omnitarg.
One women stopped taking T-DM1 and Omnitarg because of heart problems. One other woman died of pneumonia that seemed to be related to the cancer growing and not related to treatment. Herceptin and Omnitarg can cause serious side effects, including heart and lung problems.
It's important to know that T-DM1 and Omnitarg are not currently approved by the U.S. Food and Drug Administration to treat breast cancer.
This study is a phase I study. In phase I studies, researchers are figuring out the best way to give a new treatment, as well as the highest dose that can be given safely, without serious side effects. Phase I studies also help researchers figure out if a larger study involving more people makes sense.
Based on these promising results, doctors will continue to study the potential benefits of using T-DM1 and Omnitarg to treat breast and other cancers.
If you're being treated for advanced-stage, HER2-positive breast cancer, you and your doctor may be considering a number of treatment options, especially if the cancer has stopped responding to standard treatments. If you're willing to participate in a clinical trial, you may have even more options available, possibly including experimental treatments such as T-DM1 and Omnitarg. Talk to your doctor about clinical trials that might be a good fit for you and your unique situation. Visit the Breastcancer.org Clinical Trials pages for more information.