OBJECTIVE:To explore the potential correlation between clinical efficacy of pemetrexed in the treatment of ad-vanced breast cancer and TS mRNA expression. METHODS:Patients with advanced breast cancer were recruited in our study. Three cycles of pemetrexed was given to these patients,TS mRNA expression of their tumor tissues were detected. The relationship of ther-apeutic efficacies of different chemotherapy with TS mRNA expression were observed and compared during the study period. RE-SULTS:58 patients received pemetrexed chemotherapy and therapeutic efficacies of them were evaluated. One patient (1.7%) had complete response,19 patients(32.8%)had partial response,31 patients(53.4%)had stable response and 7 patients(12.1%)has progressive disease. Objective response rate was 34.5%,and disease control rate was 87.9%. TS mRNA expression level of 55 pa-tients with completed TS mRNA expression analysis varied from 0.04 to 5.11,with a median of 0.62. Mann-Whitney rank test showed that,responders had lower TS mRNA expression than nonsponders at all visits,there was statistical significance (P<0.05). Chi-square test showed that patients with low expression level of baseline(before chemotherapy)TS mRNA had significantly higher objective response rate(63.3%)than those with high expression(36.7%),there was statistical significance(P<0.05). CON-CLUSIONS:TS mRNA expression level is related to therapeutic efficacy of pemetrexed,which may be useful for predicting thera-peutic efficacy of pemetrexed therapy in patients with advanced breast cancer.