Background The Trastuzumab for Gastric Cancer (ToGA) study is the first international trial to include Japanese patients with human epidermal growth factor 2 (HER2) positive advanced/metastatic gastric or gastroesophageal junction cancer. ToGA showed that trastuzumab plus chemotherapy (capecitabine/cisplatin or 5-fluorouracil/cisplatin) improved overall survival in the overall population (hazard ratio 0.74). Regional differences in outcome in favor of Japanese populations were observed in other studies; therefore, subgroup analyses of ToGA may contribute to the evaluation of the potential benefits of this regimen in Japanese patients. Methods We performed subgroup analyses on 101 Japanese patients enrolled into ToGA (trastuzumab plus chemotherapy, n = 51; chemotherapy, n = 50). Results Median overall survival in the Japanese subgroup was 15.9 months (95% confidence interval 12-25) for trastuzumab plus chemotherapy and 17.7 months (95% confidence interval 12-24) for chemotherapy (hazard ratio 1.00; 95% confidence interval 0.59-1.69). After adjusting Presented in part at the American Society of Clinical Oncology for prespecified covariates, the estimated hazard ratio for overall survival was 0.68 (95% confidence interval 0.36-1.27). Further post hoc and exploratory examinations supported the robustness of the adjusted hazard ratios. Conclusions After adjusting for imbalanced patient backgrounds between arms, overall survival of Japanese patients with human epidermal growth factor 2 positive advanced/metastatic gastric or gastroesophageal junction cancer who received trastuzumab plus chemotherapy was improved compared with patients who received chemotherapy alone.
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