Clinical efficacy of S-1 in pretreated metastatic breast cancer patients

Background: S-1, an oral fluoropyrimidine carbamate, is an active and well-toleratedagent against solid cancer. However, the clinical efficacy ofS-1 in patients with metastatic breast cancer has not been determined. Methods: We retrospectively evaluated the efficacy of S-1 and identifiedits adverse effects in patients with metastatic breast cancerwho had failed to respond to prior chemotherapy regimens. Allthe patients were treated at the National Cancer Center Hospitaland received S-1 twice daily at a dose of 80 mg/m² for4 weeks, followed by a 2-week rest interval. Results: Between 2003 and 2007, 37 women with metastatic breast cancerreceived S-1 as a third line or greater chemotherapy regimen.All the patients had been previously treated with both anthracyclinesand taxanes prior to S-1 chemotherapy. The median order of S-1administration was as a fifth-line treatment, and 23 patients(62%) received S-1 as their final anticancer drug. One (3%)partial response and two (5%) stable diseases were observed.The median time to progression (TTP) was 84 days. Grade 2 adverseevents, such as diarrhea, stomatitis and neutropenia occurredin 5 (16%), 1 (3%) and 1 (3%) patients, respectively. Conclusions: S-1 was safety administered to heavily treated metastatic breastcancer patients with limited efficacy. Further evaluation ofS-1 is necessary to elucidate its clinical role in breast cancertreatment.