A Trial Comparing S1 Generic With Capecitabine in Metastatic Breast Cancer (MBC)

Inclusion Criteria: * Histologically confirmed breast cancer * Pretreated metastatic breast cancer not more than 2 lines chemotherapy * Have not been previously treated with capecitabine,oral fluracil * ECOG performance status of ≤ 1 * Be female and ≥ 18 and ≤ 75 years of age * Have at least one target lesion according to the RECIST criteria 1.1 Exclusion Criteria: * Pregnant or lactating women * ECOG ≥ 2 * Have been treated with capecitabine * Evidence of CNS metastasis * History of another malignancy within the last five years except cured basal cell carcinoma of skin and carcinoma in-situ of uterine cervix or a contralateral breast cancer * Abnormal laboratory values: hemoglobin \< 10.0 g/dl, absolute neutrophil count \< 1.5×10\^9/L, platelet count \< 100×10\^9/L, serum creatinine \> upper limit of normal (ULN), serum bilirubin \> ULN, ALT and AST \> 5×ULN, AKP \> 5×ULN * Serious uncontrolled intercurrent infection * Life expectancy of less than 3 months