HER2, or human epidermal growth factor 2, is a special protein (receptor) on the surface breast cancer cells, and it controls the growth of the cancer cells. The HER2 protein is present as a result of overexpression or amplification of the oncogene ERBB2. A tumor is considered HER2 positive by either the presence of HER2 protein presence and/or the overexpression of HER2 gene (the ERBB2). HER2 positive tumors are considered aggressive and have a tendency to recur, however, there are newer medications targeting HER2-positive cancer and led to significant improvement in outcome. 15% to 20% of all invasive breast cancer is reported to be HER2 positive. In this post, I will discuss the treatment of metastatic HER2 positive disease only, the nonmetastatic disease will be presented at a later date.
her2 testing must be done on biopsy material of metastatic site in all patients.