[Two cases of unresectable advanced gastric cancer treated with S-1, CDDP and trastuzumab].

We report two cases of unresectable advanced gastric cancer treated with S-1, CDDP and trastuzumab. A significant reduction of tumors was observed in these cases. A 77-year-old man was diagnosed as unresectable gastric cancer. The pathological diagnosis was tub2 and human epidermal growth factor receptor 2(HER2)positive(3+IHC method). We started chemotherapy(S-1+CDDP+trastuzumab). After 2 courses of S-1+CDDP, the findings of upper gastrointestinal endoscopy and CT were much improved to PR. But after 6 courses of S-1+CDDP, they worsened to PD. The regimen of chemotherapy was changed to weekly paclitaxel. The other patient, a 68-year-old woman, was diagnosed as far advanced gastric cancer. The pathological diagnosis was tub2=por2 and HER2 positive(3+IHC method). We started chemotherapy(S- 1+CDDP+trastuzumab). After 3 courses of S-1+CDDP, the tumor reduced significantly to PR. We continued this regimen. From the result of the ToGA trial, addition of trastuzumab to chemotherapy(capecitabine+CDDP or fluorouracil+CDDP) has been recommended as a new standard first-line regimen for HER2-positive advanced gastric cancer. But there is no evidence that trastuzumab added to the other regimen improved survival in patients with advanced gastric cancer. It is necessary to conduct a clinical trial to evaluate the treatment effect of this chemotherapy.