Efficacy of S-1 plus cisplatin combination chemotherapy in patients with HER2-positive advanced gastric cancer

Combination chemotherapy with trastuzumab and cisplatin plus capecitabine or 5-fluorouracil has been used as a standard regimen for HER2-positive gastric cancer (GC) since the Trastuzumab for Gastric Cancer (ToGA) trial. Before the ToGA trial, HER2-positive GC in Japan was treated with S-1 plus cisplatin (SP). The primary objective of this retrospective study was to explore the efficacy of SP in HER2-positive GC. We reviewed patients who had received SP as first-line chemotherapy at our institute between April 2007 and March 2011 and from whom we had enough samples to examine HER2 status. Seventy-seven patients fulfilled the selection criteria and were tested for HER2 status with immunohistochemical staining (IHC) and fluorescence in situ hybridization. The patients' backgrounds were investigated to evaluate the clinicopathologic features of their HER2-positive GC, including survival. Seven (9.1 %) of 77 patients were judged to be IHC3+, and all of these had predominantly differentiated histology. HER2 positivity was associated with differentiated histology (P = 0.016) and liver metastasis (P = 0.025). Median overall survival was 23.6 months [95 % confidence interval (CI) 0.8-44.7] in HER2-positive GC and 12.9 months (95 % CI 8.3-17.5) in HER2-negative disease, but the difference was not statistically significant (P = 0.615). In multivariate analysis, HER2 status was not associated with survival outcomes. Because of the retrospective nature of this study, we cannot conclude whether HER2 status influences the survival of patients who receive SP as first-line chemotherapy. Our study provides important historical data for prospective phase II studies of SP plus trastuzumab.