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Guidelines for sites linking to mayoclinic.orgUp to 20 percent of breast cancers produce an abnormal amount of human epidermal growth factor receptor 2 (HER2), a protein that helps drive the cancer's growth. HER2 is found on some types of breast and ovarian cancer cells.
A simple test of breast cancer cells can determine whether they produce too much HER2. Mayo Clinic specialists may treat cancer cells that produce excessive HER2 with medication targeted against HER2, such as lapatinib and trastuzumab or Herceptin.
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