[Her2 a paradigm for targeted therapy].

Fifteen percent of breast cancers overexpress Her2, a tyrosin-kinase receptor. Because of its prognosis and its incidence, several efforts have been done in the last years to better understand mechanisms of Her2 action. This led to the development of targeted therapies such as trastuzumab, monoclonal antibody directed against the Her2 extra-cellular domain. Trastuzumab provides significant clinical benefit in women with Her2-positive breast cancers. However, many women will either not respond or progress despite this treatment. The aim of this article is to summarize mechanisms of action of Her2 and of trastuzumab, and to better understand pathways activated in resistant tumors in order to identify ways to overcome them.