A phase II study of radical surgery followed by postoperative chemotherapy with S-1 for gastric carcinoma with free cancer cells in the peritoneal cavity (CCOG0301 study)

Abstract 

Background

Patients with gastric cancer who have positive cytologic results for cancer cells in peritoneal washings (CY1) have poor outcomes, even in the absence of other distant metastases. A standard treatment for such patients remains to be established.

Methods

We conducted a phase II trial with the 2-year survival rate as the primary endpoint. Patients who had gastric cancer with CY1 status but no other residual disease received postoperative chemotherapy with S-1 (1M tegafur–0.4M gimestat–1M otastat potassium) at a daily dose of 80mg/m² for 4 weeks, followed by 2 weeks of rest. This cycle was continued until disease progression or intolerable adverse events. D2 dissection was the recommended surgical procedure; splenectomy could be omitted at the discretion of the surgeon. Accrual of 50 patients was planned, and a 2-year survival rate of more than 36% was needed to exceed the historical control.

Results

Forty-eight patients were enrolled, among whom 47 were assessable for survival and 46 for adverse reactions. Median overall survival was 705 days, and progression-free survival was 376 days. The 2-year survival rate was 47%. Median time to treatment failure was 288 days. Neutropenia was the commonest ≥grade 3 toxicity (6 patients), and anorexia was the most frequent ≥grade 2 non-hematologic toxicity (10 patients).

Conclusions

Gastrectomy followed by S-1 monotherapy resulted in survival that surpassed historical data and can serve as an active control treatment for future trials in patients who have gastric cancer with CY1 status in the Far East.

Keywords: Gastric cancer, S-1, Cytologic examination, Peritoneal carcinomatosis