Herceptin May Destroy Cancer Stem Cells

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Herceptin (chemical name: trastuzumab) is a targeted therapy used to treat both early-stage and advanced-stage HER2-positive breast cancer. A study suggests that HER2-negative breast cancers also might benefit from Herceptin. These results were reported at the 2010 American Association of Cancer Research annual meeting.

HER2-positive cancers make too much of the HER2 protein (researchers call this overexpressing the HER2 gene). The HER2 protein sits on the surface of cancer cells and receives signals that encourage breast cancer cells to grow and spread. About one out of every four breast cancers is HER2-positive. Both Herceptin and the targeted therapy Tykerb (chemical name: lapatinib) work by blocking the HER2 protein's ability to make HER2-positive breast cancers grow.

Breast cancer stem cells are a new target for researchers looking for better ways to treat breast cancer. Breast cancer stem cells are sometimes called "mother" cells -- they make other breast cancer stem cells and regular breast cancer cells. Breast cancer stem cells make up about 1% of all cells in a breast cancer tumor.

This lab study used a model of how breast cancers grow. The model also included information on cancer stem cells: how they contribute to cancer growth and respond to treatment. The model helped researchers estimate how Herceptin might affect breast cancer stem cells. The model assumed that even HER2-negative breast cancers have some cancer stem cells that make too much of the HER2 protein, which may be why HER2-negative breast cancers seem to respond to Herceptin.

The results suggest that Herceptin might be able to destroy just about all cancer stem cells in breast cancer -- the length of treatment seems to depend on whether the cancer is HER2-positive or HER2 negative:

  • about 1 year of Herceptin for HER2-positive breast cancer
  • 3 to 4 years of Herceptin for HER2-negative breast cancer

It's important to know that these results are based on a model using math equations, not research in people diagnosed with breast cancer. Still, doctors have noticed that some HER2-negative breast cancers respond to treatment with Herceptin. Studies now are looking at whether Herceptin might be used to treat women diagnosed with HER2-negative breast cancer. More research is needed before doctors fully understand how Herceptin might be used to treat HER2-negative breast cancer.

Stay tuned to Research News from Breastcancer.org to learn about new findings that might help doctors use treatments we have now in new and different ways.

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