S-1, an oral fluoropyrimidine, is just as effective in terms of overall survival as a taxane as first-line treatment for patients with metastatic breast cancer, a new study published online ahead of print in the journal The Lancet Oncology has shown.1

Although oral fluoropyrimidine like capecitabine are used for the first-line treatment of metastatic breast cancer in order to avoid severe adverse events, clear evidence for this approach is lacking. Therefore, researchers sought to assess whether S-1 is noninferior to taxanes in this setting.

For the open-label, phase 3 trial, researchers in Japan enrolled 618 patients with human epidermal growth factor receptor 2 (HER2)-negative breast cancer who were resistant to endocrine therapy and had received no chemotherapy for advanced disease.

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Patients were randomly assigned 1:1 to receive a taxane (docetaxel or paclitaxel every 3 to 4 weeks or paclitaxel weekly) or S-1 orally twice daily for 28 consecutive days, followed by a 2-week break.

Results showed that after a median follow-up of 34.6 months, median overall survival was 35.0 months (95% CI: 31.1-39.0) with S-1 compared with 37.2 months (95% CI: 33.0-40.1) with a taxane (HR, 1.05; 95% CI: 0.86-1.27; Pnon-inferiority=.015).

In regard to safety, the most common grade 3 or higher adverse events in the S-1 group were neutropenia, fatigue, and edema.

“S-1 should be considered a new option for first-line chemotherapy for patients with HER2-negative metastatic breast cancer,” the authors conclude.


1. Takashima T, Mukai H, Hara F, et al. Taxanes versus S-1 as the first-line chemotherapy for metastatic breast cancer (SELECT BC): an open-label, non-inferiority, randomised phase 3 trial [published online ahead of print November 23, 2015]. Lancet Oncol. doi:10.1016/S1470-2045(15)00411-8.