[Predictive diagnosis of HER2 in gastric adenocarcinoma]

Trastuzumab is a monoclonal antibody directed against the human epidermal growth factor receptor 2 (HER2). This receptor is overexpressed in approximately 20% of gastric adenocarcinomas. The overexpression is associated with a worse prognosis, but on the other hand, patients with HER2-positive cancers were shown to benefit from the addition of trastuzumab to standard chemotherapy. To begin the targeted therapy with trastuzumab, HER2 testing is now mandatory with immunohistochemistry being the primary test followed by in situ hybridization analysis of HER2 amplification in cases with equivocal immunopositivity (score 2+). The immunohistochemical HER2 scoring system has been modified to include incomplete basolateral and lateral membrane staining, and to differentiate between surgical and endoscopical samples of the tumor. Benefit from trastuzumab treatment can be expected in tumors showing an immunohistochemical score 3+, and in cases with score 2+ and a positive finding of HER2 amplification. Clinical trials with further monoclonal antibodies and receptor tyrosine kinase inhibitors are recently ongoing to broaden the spectrum of possibilities of a multitargeted approach to the treatment of gastric cancer.