[Breast cancer and herceptin].

HER2 is a member of tyrosine kinase growth factor receptor family. When activated, it induces an intracellular phosphorylation cascade leading to an increased protein transcription and cellular growth. HER2 is overexpressed or amplified in 20 to 30% of invasive breast cancer where it plays an important role in the natural history of the disease. It is considered a poor prognostic factor and may also play a role as a predictive factor for response to therapy (potential resistance to hormonotherapy or CMF, sensitivity to anthracycline-based therapy). On the other hand, a monoclonal antibody, targetting specifically HER2, Herceptin (trastuzumab) has been developed and has shown a survival benefit in metastatic breast cancer strongly overexpressing HER2. Herceptin is actually "incorporated" in therapeutic algorithms for metastatic breast cancer and is evaluated in adjuvant settings. For all those reasons, the tumor HER2 status should probably be "routinely" tested in order to optimize the management of breast cancer patients. Nevertheless, some points remain to be elucidated, including the optimal methods of detection of HER2 (immunohistochemistry, Fish). One of the priorities for future research is to standardize HER2 testing, in order to reduce false-positive results and false-negative results and to better identify patients who are most likely going to benefit from Herceptin.