The Guideline for Breast Cancer Treatment, 2004 version, recommends chemotherapy, including anthracyclines or taxanes as a first-line chemotherapy for metastatic or recurrent (grade B recommendation) breast cancer. In a second-line therapy recommended for metastatic or recurrent diseases, the Guideline reports that a combination of capecitabine, a 5Fu derivative (an oral chemotherapy of pyrimidine fluorides approved in 2003) with docetaxel is superior to docetaxel alone for improving survival. This regimen is recommended for patients with cardiac malfunction who cannot be treated with anthracyclines (grade B recommendation). However, data are lacking to support capecitabine as a standard regimen as a second-line therapy; its efficacy needs verification and further study. Accordingly, this study is designed to investigate the efficacy and safety of S-1 alone, an oral pyrimidine fluoride, to which an indication of "inoperable or recurrent breast cancer" was added, as a first-line therapy in patients with inoperable or recurrent breast cancer by comparing it with Capecitabine alone, which is already approved of the same indication.