[S-1 monotherapy achieved twenty-month survival for peritoneal lavage cytology-positive gastric cancer patient undergoing noncurative resection].

: We report a gastric cancer patient with positive peritoneal lavage cytology (CY1) who achieved 20-month progression free survival by S-1 monotherapy. An 82-year-old male patient who underwent distal gastrectomy with residual disease for type 4 scirrhous gastric cancer manifesting pyloric stenosis, direct invasion to the pancreas, and CY1. He received S-1 monotherapy postoperatively. His ECOG performance status (PS) was 0. The initial treatment schedule was 100mg/day, twice daily for 4 weeks with a 2-week rest, repeated every 6 weeks. Grade 2 thrombocytopenia at the end of the 5th course of treatment required discontinuation of one course of treatment, and subsequent treatment was continued with a dose reduction to 80mg/day. Afterwards, although treatment was temporarily postponed for 2 weeks, the dose modification enabled him to receive S-1 for 20 months, leading to a relative dose intensity of 81%. There was no evidence of disease progression. The most severe adverse events were transient grade 3 neutropenia as well as leukocytopenia, anemia, and thrombocytopenia, grade 2 each, without gastrointestinal toxicities. His PS was not deteriorated. Although survivalrates of CY1 gastric cancer patients are still poor, our case suggests that S-1 monotherapy is effective against CY1, even for patients aged over 80, if the relative dose intensity is maintained by comprehensive patient management and appropriate dose modification.