A phase III trial comparing oral S-1/cisplatin and intravenous 5-fluorouracil/cisplatin in patients with untreated diffuse gastric cancer

The effect of histology-based treatment regimen on diffuse gastric adenocarcinoma has not been evaluated in clinical trials. This international phase III trial evaluated the efficacy and safety of S-1 (a contemporary oral fluoropyrimidine)/cisplatin versus 5-fluorouracil (5-FU)/cisplatin in chemotherapy-naïve patients with diffuse-type adenocarcinoma involving the gastroesophageal junction or stomach. Patients and methods: Eligibility criteria included untreated, measurable, advanced diffuse adenocarcinoma confirmed by central pathology and performance status of 0-1. Patients were randomized (2: 1) to receive S-1/cisplatin or 5-FU/cisplatin. Primary end point was overall survival (OS), and secondary end points were progression-free survival, time to treatment failure, overall response rate, and safety. A multivariable analysis was also carried out. Results: Overall, 361 patients were randomized (S-1/cisplatin, n=239; 5-FU/cisplatin, n=122); half (51%) were men, and median age was 56.0 years. In each group, median number of treatment cycles per patient was 4 (range, S-1/cisplatin: 1-20; 5-FU/cisplatin: 1-30), and dose intensity was >95%. OS was not different in the two groups (median OS with S-1/cisplatin, 7.5 [95% confidence interval (CI): 6.7, 9.3]; 5-FU/cisplatin, 6.6 [95% CI: 5.7, 8.1] months; hazard ratio, 0.99 [95% CI: 0.76, 1.28]; P=0.9312). Overall response rate was significantly higher in the S-1/cisplatin than 5-FU/cisplatin group (34.7% versus 19.8%; P=0.01), but progression-free survival and time to treatment failure were not different. Safety was similar between the 2 groups; however, fewer patients treated with S-1/cisplatin than 5-FU/cisplatin had≥1 grade 3/4 treatment-emergent adverse event or≥1 adverse event resulting in treatment discontinuation. One treatment-related death occurred in each group. Slow accrual led to early termination. Conclusions: These data suggest that S-1/cisplatin and 5-FU/cisplatin are similar in efficacy and safety in untreated patients with advanced diffuse adenocarcinoma of the gastroesophageal junction or stomach. The primary end point was not met.