All women with advanced breast cancer face a difficult and uncertain future. Most of them endure long courses of treatment that leave them looking to alternative or experimental therapies for a cure. A drug called trastuzumab attacks a particularly aggressive form of breast cancer in a unique way.
One aggressive form of breast cancer is characterized by too much of a protein known as human epithelial growth factor receptor-2 (HER2). This protein stimulates the growth of breast tumors. Trastuzumab is a monoclonal antibody, which blocks the HER2 receptor. This obstructs the growth of cancer cells.
Scientists have known since the 1980's that women whose breast cancers produce too much HER2 have cancers that are more aggressive and more likely to metastasize, or spread. Trastuzumab can enhance the effectiveness of standard chemotherapy treatments by targeting the HER2 receptor and slowing its activity.
Several clinical studies show that women with HER2-positive tumors using trastuzumab with chemotherapy have slower cancer growth and better response to treatment. An early study from 2001 showed that trastuzumab when added to chemotherapy was effective in slowing disease progression in HER2-positive breast cancer patients. In women with HER2-positive operable breast cancer, trastuzumab combined with chemotherapy improved survival outcome compared to those without trastuzumab.
Combined results of 2 studies involving over 3,300 women found longer survival rates after 1 year of treatment with trastuzumab added to chemotherapy compared to those without trastuzumab.
In another study (the HERA trial), 1 year of treatment resulted in significant survival and less disease progression. In follow-up studies at 2 and 4 years, disease-free survival was maintained. Women who began treatment with trastuzumab after the first year of the study had similar results. There was little difference however, in overall survival or risk of death at the 4 year follow-up.
Unfortunately, although trastuzumab may be able to slow the growth of cancer cells, it is also associated with some serious side effects.
Cardiomyopathy is a potentially life-threatening heart muscle weakness that can lead to heart failure. This side effect is particularly common in women receiving chemotherapy with anthracyclines and cyclophosphamide. For this reason, woman considering trastuzumab have a thorough cardiac assessment before taking the drug and during treatment.
Other serious side effects include:
More common side effects include:
Trastuzumab is used only in cancers that overproduce HER2. It is now used for:
American Cancer Society
National Cancer Institute
Canadian Cancer Society
Canadian Breast Cancer Foundation
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Last reviewed October 2016 by Michael Woods, MD
Last Updated: 11/14/2014