Inclusion Criteria

          -  Patients have voluntarily agreed to participate and given written informed consent.

          -  Male or female ≥18 years of age on day of signing the informed consent form (ICF).

          -  Histologically or cytologically confirmed adenocarcinoma of the breast.

          -  Recurrent disease not amenable to curative surgery or radiation therapy, or metastatic
             disease with an indication for a taxane-containing therapy.

          -  Availability of formalin-fixed paraffin-embedded (FFPE) tissue block from the primary
             tumor, or a metastatic lesion, to confirm HER2-positivity by the central laboratory,
             based on FISH amplification ratio ≥2.0 or IHC score 3+, and for hormone status
             (ER/PgR) determination (local or central laboratory). If not possible, a fresh biopsy
             is required.

          -  No prior systemic anticancer agent such as chemotherapy, biological or targeted agent
             for metastatic disease with the exception of hormonal therapy, which must be stopped
             at least 2 weeks before randomization. Use of herbal remedies or traditional Chinese
             medicines for anticancer, hematologic or liver function, or anti-infective treatment
             must be stopped at the time of the ICF signature (at least 2 weeks before
             randomization).

          -  For patients with recurrent disease, prior neo-/adjuvant therapy containing
             trastuzumab and/or lapatinib must have been stopped at least 12 months before the
             diagnosis of recurrent (local or metastatic) disease. If trastuzumab/lapatinib was not
             used, prior neo-/adjuvant therapy with a taxane must have been stopped at least 6
             months before the diagnosis of recurrent (local or metastatic) disease. If only other
             cytotoxics were given, they must be stopped at least 4 weeks before randomization. Any
             hormonal therapy must be stopped at the time of the ICF signature.

          -  Measurable disease (at least one measurable target lesion assessed by CIR; bone-only
             or central nervous system [CNS]-only metastases are not allowed).

          -  Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.

          -  LVEF within institutional range of normal at baseline (within 42 days before
             randomization) as determined by either echocardiography (ECHO) or multigated
             acquisition (MUGA) scan.

          -  Adequate hematologic, hepatic and renal function as indicated by the following
             laboratory values:

          -  Absolute neutrophil count (ANC) ≥1,500/μL without granulocyte-colony stimulating
             factor (G-CSF) or other medical support

          -  Platelets ≥100,000/μL

          -  Hemoglobin ≥9 g/dL without transfusion or other medical support within 14 days

          -  Serum creatinine ≤1.5 x upper limit of normal (ULN) and creatinine clearance rate ≥50
             mL/min, calculated according to Cockroft-Gault formula

          -  Serum total bilirubin ≤1.5 x ULN (unless the patient has documented ·Gilbert's
             syndrome) without any medical support within 14 days

          -  Serum aspartate aminotransferase/glutamicoxaloacetic transaminase (AST/SGOT) or serum
             alanine aminotransferase/glutamate-pyruvate transaminase (ALT/SGPT) ≤2.5 x ULN (≤5 x
             ULN in the case of liver metastases) provided alkaline phosphatase (ALK) is ≤2.5 x
             ULN. In the case of bone metastasis, serum ALK can be >2.5 x ULN if AST and ALT are
             ≤1.5 x ULN without any medical support within 14 days

          -  International normalized ratio (INR), and activated partial prothrombin time (aPTT) or
             partial prothrombin time (PTT) ≤1.5 x ULN.

          -  Estimated life expectancy ≥3 months.

          -  Female patients are eligible to enter and participate in the study if they are of:
             Non-childbearing potential. Childbearing potential, have a negative serum pregnancy
             test at Screening, are not breast feeding, and use highly-effective or acceptable
             contraceptive measures before study entry and throughout the study until 7 months
             after the last investigational/comparator product administration. Highly-effective or
             acceptable contraceptive measures.

          -  Male patients with partners of childbearing potential are eligible to enter and
             participate in the study if they, and their female partners, are willing to use
             highly-effective or acceptable contraceptive measures before study entry and
             throughout the study until 7 months after the last investigational/comparator product
             administration.

        Exclusion Criteria

          -  Previously- or currently-treated (systemic chemotherapy, biological, or targeted
             agent, or any other anticancer agent) metastatic breast cancer with the exception of
             hormonal therapy.

          -  Known brain metastasis or other CNS metastasis that is either symptomatic or
             untreated. Central nervous system metastases that have been treated by complete
             resection and/or radiotherapy demonstrating stability or improvement are not an
             exclusion criterion provided they are stable as shown by computed tomography (CT) scan
             for at least 4 weeks before Screening without evidence of cerebral edema and no
             requirements for corticosteroids or anticonvulsants.

          -  Participation in another clinical study within 4 weeks before enrollment (3 months for
             studies involving monoclonal therapy) or the intention of participating in another
             clinical study during any part of the study period.

          -  History of other malignancy within the last 5 years, except for carcinoma in-situ of
             the cervix, basal cell carcinoma or squamous cell carcinoma of the skin that has been
             previously treated with curative intent.

          -  Known history of human immunodeficiency virus (HIV). Clinically significant active
             infection requiring therapy; positive tests for hepatitis B; or hepatitis C.

          -  Underlying medical conditions or current severe, uncontrolled systemic disease that,
             in the Investigator's opinion, will make the administration of study drug hazardous. A
             major surgical procedure within 4 weeks prior to enrollment or anticipation of the
             need for major surgery during the course of study.

          -  Current uncontrolled hypertension (systolic >150 mmHg and/or diastolic >100 mmHg) or
             unstable angina.

          -  History of chronic heart failure based on any New York Heart Association (NYHA)
             criteria, or left ventricular hypertrophy. Current serious cardiac arrhythmia
             requiring treatment or clinically significant conduction defects as seen on
             electrocardiogram (ECG). History of myocardial infarction within 6 months of
             randomization. History of LVEF decline to below 50% during or after previous
             trastuzumab neo-adjuvant or adjuvant therapy. Significant cardiac murmurs either on
             examination or ECHO.

          -  History of prior exposure to doxorubicin >360 mg/m² (or equivalent). Use of oral,
             injected or implanted hormonal methods of contraception. Chronic daily use of
             corticoids (equivalent to >10 mg/day methylprednisolone) by oral intake (inhalation is
             permitted).

          -  Known hypersensitivity to any of the study drugs.

          -  Residual non-hematologic toxicity ≥ Grade 2 from prior therapy.