[HER2 and gastric cancer. Recommendations for clinical practice in 2011]

Trastuzumab in combination with capecitabine or 5-fluorouracil and cisplatin has been approved by the European Medicines Agency (EMEA) for the treatment of patients with human epidermal growth factor receptor 2 (HER2)-positive (immunohistochemistry [IHC] 3+ or IHC 2+/ fluorescence in situ hybridization [FISH]-positive or IHC 2+/ silver in situ hybridization [SISH]-positive) metastatic adenocarcinoma of the stomach or gastro-esophageal (GE) junction. HER2 testing in gastric cancer (GC) differs from testing in breast cancer (BC) due to major differences in the tumor biology; as the disease is progressing rapidely, we recommend to test every GC at diagnosis and to offer a rapid testing (less than five days) in the metastatic setting. IHC should be the initial testing methodology and FISH or SISH should be used to retest IHC 2+ samples. As GC more frequently shows incomplete membrane staining and focal staining for HER2, HER2 testing guidelines have been adapted from BC protocols. The scoring system is slightly different in respect to the characteristics of GC. For in situ hybridization, SISH should be used in order to identify heterogeneous staining with a higher accuracy than FISH. Enrollment in training and quality assurance programs is highly recommended. In case of negativity on biopsy, it is recommended to retest for HER2, when possible, on surgical specimens and/or metastasis. This will ensure accurate and consistent HER2 testing results, which will allow the appropriate selection of patients eligible for treatment with trastuzumab.