Trastuzumab is a fully humanised monoclonal antibody directed at the human epidermal growth factor receptor-2 (HER-2) which has been a component of standard therapy for advanced and resected HER-2-positive breast cancers for almost a decade. HER-2 over-expression, defined as HER-2 protein over-expression using immunohistochemistry scored as 3+ and/or erbB-2 amplification detected by fluorescent in situ hybridisation, was detected in 22.1% of 3807 patients with advanced gastric and oesophagogastric junction (OGJ) adenocarcinoma screened for eligibility for the phase III ToGA study. The validated scoring system for HER-2 positivity in gastric cancers differs from that recommended for breast cancer due to an increased frequency of incomplete membranous immunoreactivity and heterogeneity of HER-2 expression in gastric cancers. The highest rates of HER-2 over-expression are observed in patients with OGJ rather than gastric tumours and intestinal-type rather than diffuse or mixed histology. The international multicentre randomised phase III ToGA study assessed the addition of trastuzumab to a cisplatin plus fluoropyrimidine (FP) chemotherapy doublet for patients with HER-2-positive advanced gastric or OGJ adenocarcinoma. The investigators reported a clinically and statistically significant benefit in terms of response rate (47.3% versus 34.5%, p=0.0017), median progression-free survival (6.7 versus 5.5 months, p=0.0002) and median overall survival (13.8 versus 11.1 months, p=0.0046). Trastuzumab plus FP chemotherapy is now the standard of care for patients with advanced gastric and OGJ cancers which over-express HER-2. Further research to evaluate trastuzumab delivered beyond progression, in combination with alternative first-line chemotherapy regimens, and in the perioperative and adjuvant setting is urgently needed. Additionally, research into mechanisms of resistance and strategies to overcome primary or acquired resistance to trastuzumab must now be expedited, using lessons learnt over the past decade in HER-2-positive breast cancer to maximise the benefit from this agent.
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