A phase I study of combination therapy of the oral fluorinated pyrimidine compound S-1 with low-dose cisplatin twice-a-week administration (JFMC27-9902 Step2) in patients with advanced gastric cancer using a continual reassessment method.

OBJECTIVE We conducted a Phase I study to evaluate the safety and efficacy of a combination of S-1 with semi-weekly low-dose cisplatin in patients with unresectable/recurrent gastric cancer to determine the recommended dose (RD) for a subsequent Phase II study. METHODS S-1 was administered orally at 80-120 mg/body/day based on body surface area. One cycle consisted of the consecutive administration of S-1 for 28 days followed by 14 days rest. Three dose levels, 7.5, 10, and 15 mg/m(2)/day, were set for cisplatin, which was administered twice-a-week for 4 weeks followed by 2 weeks of rest in each cycle. Dose-limiting toxicity (DLT) data were continually monitored to enable decisions regarding cisplatin dose escalation and deescalation based on a new dose-finding algorithm using a continual reassessment method (CRM). The CRM target toxicity level to estimate the RD was set at 20%. RESULTS Eight and five patients were treated at cisplatin dose levels of 10 and 15 mg/m(2)/day, respectively. Two DLTs occurred at both dose levels. On the basis of this data, the CRM estimated the RD to be 10 mg/m(2)/day of cisplatin. Three patients of eight patients treated with 10 mg/m(2)/day of cisplatin exhibited a confirmed partial response during the treatment period. CONCLUSION For future trials examining the safety and efficacy of daily S-1 with semi-weekly cisplatin in patients with unresectable/recurrent gastric cancer, we found a cisplatin RD of 10 mg/m(2)/day.