A study found that some metastatic breast cancers that had stopped responding to many treatments did respond to an experimental treatment that's a combination of Herceptin (chemical name: trastuzumab) and a chemotherapy medicine called maytansine. These results were presented at the 2009 San Antonio Breast Cancer Symposium.
Herceptin is a targeted therapy medicine already approved by the U.S. Food and Drug Administration 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 isn't considered a targeted medicine, which means it can affect healthy cells as well as cancer cells.
The 110 women in this study had received a number of treatments for metastatic breast cancer but the cancer either didn't respond or stopped responding to the treatments. Many of the women already had been given Herceptin and Tykerb (chemical name: lapatinib), another targeted therapy medicine for HER2-positive cancers. Most of the cancers were HER2-positive.
The women were given the experimental combination of Herceptin and maytansine, known as T-DM1 (chemical name: ado-trastuzumab emtansine). T-DM1 was designed to deliver the chemotherapy medicine to cancer cells in a targeted way by attaching the chemotherapy medicine to the Herceptin. Herceptin then carries the chemotherapy medicine to the cancer cells.
Even though the women in the study already had been treated with a number of other medicines (heavily pretreated), some did respond to T-DM1.
Nearly half (44.5%) the women either stayed stable or improved for 28 days or more (called clinical benefit). This clinical benefit lasted from 1.2 to 8.4 months.
- 32.5% of the women showed some improvement, rather than just staying stable
- women diagnosed with HER2-positive breast cancer benefited the most: 52.6% of them got clinical benefit
- the time the women lived without the cancer growing (called progression-free survival) was as high as 11.7 months and averaged about 7 months
Less than 25% of the women had serious side effects. Most of the serious side effects were related to the chemotherapy part of the treatment and 5.5% of the women stopped treatment because of side effects. Herceptin can cause heart damage and can lead to heart failure. Only two women in this study had some decrease in heart function, but they didn't have heart failure.
These results are encouraging, especially since the cancers had stopped responding to so many other treatments. It's also interesting that Herceptin seemed to be effective against HER2-negative cancers; Herceptin is thought to work on only HER2-positive breast cancer. Still, this is a very small, early study on an experimental medicine. More research is needed before doctors understand the benefits and risks of this treatment.
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.
Editor’s Note: On Feb. 22, 2013, the U.S. Food and Drug Administration approved Kadcyla (chemical name: T-DM1 or ado-trastuzumab emtansine). In some early studies of T-DM1, such as the study reviewed here, it was reported that the chemotherapy medicine maytansine was attached to Herceptin to form T-DM1. Emtansine is a derivative of maytansine.