[Efficacy and safety of TS-1 monotherapy for advanced/metastatic breast cancer - an observational study by the Kumamoto Breast Cancer Cooperative Group(KBCCG)].

ABSTRACT

TS-1, an oral fluoropyrimidine, is known to be effective for the treatment of various carcinomas including advanced/metastatic breast cancer.The Kumamoto Breast Cancer Cooperative Group(KBCCG)conducted an observational study, wherein, the efficacy and safety of TS-1 monotherapy was analyzed in 35 patients with recurrent or metastatic breast cancer.The median time to cancer progression was 3.7 months, overall response rate was 12%, and clinical benefit rate was 32%. Adverse events were observed in 27 patients(77%), and adverse events of Grade >3 were observed in 7 patients(20%). The rate of treatment-related Grade 3 and 4 adverse events increased, and was associated with poor levels of creatinine clearance(Ccr)ie <60mL/min.This study suggests that TS-1 monotherapy can potentially be used as a salvage treatment for advanced/metastatic breast cancer owing to its safety and efficacy.Measuring the level of Ccr before TS-1 therapy should be considered to avoid severe adverse events.