Docetaxel and Cisplatin Chemotherapy With or Without High Dose Proton Pump Inhibitor in Metastatic Breast Cancer

Inclusion Criteria: * Signed informed consent. * Female, ≥ 18 years. * Histologically confirmed invasive breast cancer. * Metastatic breast cancer. * Karnofsky Performance Status ≥60. * Life expectancy of more than 3 months. * Subject must have adequate organ function. * Normal laboratory values: hemoglobin \> 80g/dl, neutrophils \> 2.0×10\^9/L, platelets \> 80×10\^9/L, serum creatinine \< upper limit of normal (ULN), serum bilirubin \< ULN, ALT and AST \< 2.5×ULN, AKP \< 5×ULN. * Negative serum pregnancy test for women with childbearing potential. * Good conditions for infusion and willing to have phlebotomy throughout whole study. * Have ceased anti-tumor treatments including endocrinotherapy and bio-targeted therapy for more than 28 days. * Have at least one target lesion according to the Response Evaluation Criteria in Solid Tumors (RECIST) criteria. * No prior use of docetaxel or has used docetaxel in adjuvant/neo-adjuvant chemotherapy and has a relapse free survival of at least 12 months. Exclusion Criteria: * Pregnant or lactating females. * History of other malignancy. However, subjects who have been disease-free for 5 years, or subjects with a history of completely resected non-melanoma skin cancer or successfully treated in situ carcinoma are eligible. * Concurrent disease or condition that would make the subject inappropriate for study participation, or any serious medical disorder that would interfere with the subject's safety. * Active or uncontrolled infection. * Known history of uncontrolled or symptomatic angina, arrhythmias, or congestive heart failure. * Concomitant with brain metastases. * Have received chemotherapy after metastasis.