Study of TS-1 as 2nd Line Treatment in Patients With Advanced Metastatic Breast Cancer

Inclusion Criteria: * Age: 18-75 years old female. * ECOG status: 0-2. * Life expectancy of ≥ 3 months. * Histologic or cytologic diagnosis of breast cancer. * Progression after receiving one standard prior chemotherapy regimen for recurrent or metastatic lesion except an endocrine regimen. * At least one measurable lesion of \>=2 cm (\>=1 cm on spiral CT scan)according to RECIST (v1.1). * Adequate organ functions: * Hematopoietic: Hemoglobin ≥90g/L, Absolute neutrophil count ≥1.5×10\^9/L, Platelet count ≥80×10\^9/L. * Biochemistry: TBil ≤1.5 times upper limit of normal (ULN), AST and ALT ≤2.5× ULN(≤5x ULN if due to liver metastases), Creatinine ≤1.0×ULN and Creatinine clearance \>50 ml/min. * Women with children potential must have negative pregnancy tests 7 days prior to enrollment and be willing to practice acceptable methods of birth control during the study and 8 weeks after last drug administered. * Ability to take oral medication . * Signed informed consent. Exclusion Criteria: * Pregnancy or lactation or no effective contraception in fertile patients. * Prior treatment with 5-FU or drugs of same class(excluding patients that relapsed more than one year after adjuvant therapy). * Less than 4 weeks since prior investigational agents. * conditions impacting oral drug taking or absorption (e.g. inability to swallow, gastrointestinal resection, chronic diarrhea, intestinal obstruction). * Organ invasion with rapid progression(e.g. lesions exceeding half of Liver or Lung). * CNS or psychiatric disorders. * Allergic to 5-FU. * Only with bone metastases and no measurable lesions. * Clinically significant heart diseases (e.g.congestive heart failure, ventricular arrhythmia, myocardial infarction) before enrollment. * Serious peptic ulcer disease or digestive disorders. * Bone marrow (Hemoglobin \<90g/dl, ANC \<1.5×10\^9/L, Platelet count \<75×10\^9/L). * Renal function disorder (Creatinine \>1.0×ULN). * Liver function disorder (TBil \>1.5×ULN). * Uncontrolled brain metastases. * Noncompliance with the study protocol.