The purpose of this study is to assess the effectiveness and safety profile of Aiyi®(Tegafur Gimeracil Oteracil Potassium Capsule, TS-1) as a second line therapy in Chinese female patients with advanced metastatic breast cancer.

Tegafur Gimeracil Oteracil Potassium Capsule is a novel oral derivative of the 5-fluorouracil(5-FU) prodrug tegafur combined with two modulators. Recent clinical trial has reported the promising effect of Tegafur Gimeracil Oteracil Potassium Capsule in metastatic breast cancer. The innovative drug, S-1, has obtained the approval of treatment of advanced breast cancer in Japan, meanwhile, Generic drug is only approved for the indication of gastric cancer in China mainland by Chinese authority, SFDA, and no Chinese clinical study data of TS-1 in breast cancer so far.

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.