A phase II study of adjuvant S-1/cisplatin chemotherapy followed by S-1-based chemoradiotherapy for D2-resected gastric cancer.

Purpose: Surgery is the only possible curative treatment for gastric cancer. However, the high recurrence rate makes gastric cancer difficult to cure by surgery alone. The present study was conducted to evaluate the clinical outcomes and toxicity of adjuvant treatment, including S-1/cisplatin chemotherapy followed by radiotherapy with concurrent S-1.

Methods: Patients with radically D2-resected adenocarcinoma of the stomach of stage IB-IV (M0) were eligible. Patients were treated with S-1 (40-60 mg depending on the patient's body surface area) twice daily for 3 weeks and cisplatin (60 mg/m(2)) intravenously on day 1 every 5 weeks. Patients received CRT (45 Gy of radiation at 1.8 Gy/day, 5 days per week, for 5 weeks with the same dose of S-1 during radiation) followed by two additional cycles of S-1/cisplatin. The primary endpoint was the 3-year disease-free survival (DFS) rate; the secondary endpoints were the 3-year overall survival rate and toxicities.

Results: Until May 2012, 46 patients were enrolled, and 34 (73.9%) completed the planned treatment. The median age was 53 years (range: 31-69 years), and the numbers of patients with stage IB, II, III and IV disease were 0, 17, 25 and 4, respectively. Main grade 3-4 toxicities were as follows: neutropenia (28.2%), nausea (17.4%), vomiting (8.7%) and anorexia (15.2%). At the time of analysis, after a median follow-up period of 56.5 months (3.03-74.0 months), 16 recurrence events and 15 deaths were reported. The estimated 3-year DFS and survival rates were 65.2 and 76.1%, respectively. The most common site of recurrence was the peritoneum (n = 12).

Conclusions: The results of this phase II study show that intensified adjuvant treatment with S-1/cisplatin chemotherapy and S-1-based chemoradiotherapy was tolerable and effective in reducing disease recurrence. The addition of radiotherapy to chemotherapy may be effective in D2-resected gastric cancer. Although the data here are promising, a randomized trial is needed between patients treated with the current regimen and an appropriate comparator arm.