T-DM1 is an experimental targeted therapy medicine that's a combination of Herceptin (chemical name: trastuzumab) and a chemotherapy medicine called maytansine.
Several small research studies found that retesting metastatic breast cancer for HER2 status -- to see if the cancer is still HER2-positive -- can help figure out if the cancer is more or less likely to respond to T-DM1. The results were presented at the 2010 American Society of Clinical Oncology (ASCO) annual meeting.
Herceptin is a targeted therapy medicine used 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 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, like some other chemotherapy medicines, disrupts the way cells grow. Maytansine on its own isn't considered a targeted medicine, 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.
Doctors expect T-DM1 to work best against HER2-positive breast cancers. Still, breast cancers that were HER2-positive in the past can change over time and become HER2-negative.
So in these studies, the researchers wanted to see if the response to T-DM1 was influenced by the HER2 status of breast cancers based on test results done around the time of T-DM1 treatment. All the cancers were HER2-positive when first diagnosed. At the time of T-DM1 treatment, all the cancers were metastatic and had been treated previously with many other medicines.
Women diagnosed with metastatic breast cancer that was still HER2-positive treated with T-DM1 lived for a little over a year (12.32 months) before the cancer started growing again (called progression-free survival). Women diagnosed with metastatic breast cancer that was now HER2-negative treated with T-DM1 lived for only 2.17 months before the cancer started growing again.
In one study, 40.8% of women diagnosed with metastatic breast cancer that was still HER2-positive responded to T-DM1, while only 20% of women diagnosed with metastatic breast cancer that was now HER2-negative responded to T-DM1. In another study, 33.8% of women diagnosed with metastatic breast cancer that was still HER2-positive responded to T-DM1, while only 4.8% of women diagnosed with metastatic breast cancer that was now HER2-negative responded to T-DM1.
These results confirm that T-DM1 works best against HER2-positive cancers. These results are promising and T-DM1 may prove to be a good new treatment for metastatic, HER2-positive breast cancers that have stopped responding to other treatments.
The results also suggest that because the characteristics of a breast cancer -- such as HER2 status -- can change over time, getting a new biopsy of a recurrent or metastatic cancer and testing for HER2 status and other characteristics can help make treatment decisions.
If you're being treated for advanced-stage 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 an experimental treatment such as T-DM1. 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.
And stay tuned to Breastcancer.org to learn about the latest research on new, better ways to treat breast cancer.
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