Background: The response rate of advanced or recurrent gastric cancer to S-1 (TS-1) is 46.5%, which is higher than the response rate of this type of cancer to any other anticancer agent. However, the incidence of adverse reactions to this drug has also been reported to be as high as 83.2%. According to a postmarketing survey, adverse reactions to this drug begin to appear 2-3 weeks after the start of drug administration. With these findings in mind, we recently devised a new dosing regimen for the drug, by which the drug is administered for 2-week periods separated by 1-week drug-free intervals (the 2-week regimen). The aim of this retrospective study was to evaluate the efficacy and feasibility of the 2-week regimen in comparison with a 4-week dosing regimen with a 2-week interval between sessions (the 4-week regimen) as the historical control.
Methods: The subjects were 27 patients with advanced or recurrent gastric cancer who received S-1 therapy at our center between September 1999 and November 2001. Of these patients, 14 who received the 4-week regimen before January 2001 served as historical controls, and the results in these patients were compared with those of the remaining 13 patients, who received the 2-week regimen after February 2001. Patient backgrounds, adverse reactions, compliance, and efficacy were investigated retrospectively.
Results: The incidence of adverse reactions tended to be lower in the 2-week-regimen group (77%) than in the 4-week-regimen group (93%). The percentage of patients who received the drug for 6 months in complete compliance with the dosing schedule, as calculated by the Kaplan-Meier method, was 85% in the 2-week-regimen group and 40% in the 4-week-regimen group. The response rate to the drug was 23% in the 2-week-regimen group and 21% in the 4-week-regimen group.
Conclusion: These results suggest that this 2-week regimen may mitigate adverse reactions and prolong the medication period.