A randomized controlled study is conducted on patients with resected gastric cancer assigned to postoperative adjuvant therapy of TS-1 alone or PSK combined with TS-1, with the objective to examine or validate the outcome, QOL and prognostic factors (host and tumor factors), and explore the factors enhancing the antitumor effect of TS-1.

The 5-year survival after gastric cancer surgery remains poor as the cancer advances to stages II, IIIA, IIIB and IV. Tegafur-gimeracil-oteracil potassium (TS-1) is used as the first line treatment for advanced and recurrent gastric cancer. But TS-1 is accompanied by an adverse drug reaction of bone marrow suppression that is not readily seen in conventional oral fluoropyrimidines. Among randomized controlled trials on postoperative adjuvant chemotherapy for gastric cancer, the beneficial results of survival rates using Krestin (PSK) in combination with chemotherapy have been reported. With the objective to enhance the antitumor effect of TS-1 and to improve the QOL of patients, we have planned to validate the clinical significance of combined PSK and TS-1 therapy as postoperative adjuvant therapy for gastric cancer, using in principle the TS-1 regimen of 2-week dosing 1-week off for 6 months followed by 2-week dosing 2-week off for 6 months.

Inclusion Criteria:

• Patients with microscopic stage II or IIIA resectable gastric cancer
• Patients who have not received preoperative cancer therapy (radiotherapy, chemotherapy or immunotherapy)
• Patients with serum immunosuppressive acidic protein (IAP) measured within 2 weeks before surgery
• Patients with no metachronous or synchronous multiple cancer
• Patients without severe impairment of renal, hepatic and bone marrow functions
• Patients who are judged to be capable of tolerating surgery
• Patients with preoperative performance status 0 to 2
• Patients with no serious concurrent complications (such as bone marrow suppression, diarrhea and infection)
• Patients who are judged to be capable of tolerating this treatment, and who have given written informed consent to participate in this study

Exclusion Criteria:

• Patients with fresh hemorrhage from the gastrointestinal tract
• Patients with retention of body fluid necessitating treatment
• Patients with infection, intestinal palsy or intestinal occlusion
• Patients who are pregnant or hope to become pregnant during the study period
• Patients with diabetes treated by continuous use of insulin or showing poor glycemic control
• Patients with a history of ischemic heart disease
• Patients with concurrent psychiatric disease or psychotic symptoms, and judged to have difficulties participating in the study
• Patients receiving continuous administration of steroids
• Patients who have experienced serious drug allergy in the past
• Others, patients judged by the investigator or subinvestigator to be inappropriate as subject