Experimental T-DM1 May Help Treat Metastatic, HER2-Positive Disease

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A small, early study suggests that T-DM1, an experimental medicine, may be a better first treatment for women diagnosed with metastatic, HER2-positive breast cancer than a combination of Herceptin (chemical name: trastuzumab) and Taxotere (chemical name docetaxel).

Women treated with T-DM1 also had fewer side effects compared to women treated with Herceptin and Taxotere. These results were presented at the 2010 annual meeting of the European Society for Medical Oncology (ESMO).

T-DM1 is a combination of Herceptin and the chemotherapy medicine maytansine; the maytansine is attached to the Herceptin, which doctors call "conjugated."

Herceptin is a targeted therapy medicine 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.

T-DM1 was designed to deliver maytansine to cancer cells in a targeted way by attaching the chemotherapy medicine to the Herceptin. Herceptin then carries the chemotherapy medicine to the HER2-positive cancer cells.

Metastatic breast cancer is cancer that has spread to other parts of the body away from the breast, such as the bones or liver.

In this study, 137 women with newly diagnosed metastatic, HER2-positive breast cancer were given one of two treatments. The women hadn't received any earlier treatments for metastatic breast cancer.

Half the women got T-DM1. The other women got a standard combination of Herceptin and Taxotere.

After about 6 months, an early analysis showed that T-DM1 was somewhat more effective than the Herceptin-Taxotere combination:

  • 48% of women who got T-DM1 showed signs that the cancer was weaker
  • 41% of women who got the Herceptin-Taxotere combination showed signs that the cancer was weaker

Severe side effects, which were mostly from chemotherapy, were much less likely in women who got T-DM1:

  • 37% of women who got T-DM1 had severe side effects
  • 75% of women who got the Herceptin-Taxotere combination had severe side effects

The study is ongoing, so the researchers will continue to compare T-DM1 to the Herceptin-Taxotere combination.

Other small, early studies have shown that some metastatic, HER2-positive breast cancers that have stopped responding to other treatments will respond to T-DM1. The study reviewed here is the first one to compare T-DM1 as the first treatment (known as first-line treatment) for metastatic, HER2-positive breast cancer to a common first-line treatment. A larger, phase III study, called MARIANNE, is being done to further evaluate T-DM1 as a first-line treatment for newly diagnosed metastatic, HER2-positive breast cancer.

If you've been diagnosed with metastatic, HER2-positive breast cancer, you and your doctor may be considering a number of treatment options. 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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