[A case of type 4 gastric cancer with peritoneal dissemination successfully treated over 2 years by alternate-day administration of TS-1].

We report a patient with unresectable advanced gastric cancer who has been being treated by TS-1 administration on alternate days for 2 years. The patient was a 50-year-old female with type 4 gastric cancer accompanied by Schnitzler metastasis and pleural effusion. TS-1 administration was initiated at a daily dose of 100 mg with a schedule of 4-week administration and 2-week suspension. However, grade 2 hepatic dysfunction and leukocytopenia developed. When the daily TS-1 administration was changed to alternate-day administration at the same dose, no side effects were observed, allowing the continuation of treatment. She has maintained a minor response (MR)-no change (NC) for 1 year and 5 months, and is still symptom-free and being treated on an outpatient basis at present, 2 years after treatment. TS-1 is an anti-cancer drug that plays a central role in chemotherapy for gastric cancer. However, in some patients, side effects sometimes develop using the routine administration method, making continuation of administration difficult. Alternate-day TS-1 administration has great potential as a protocol that produces long-term anti-tumor effects while reducing side effects.