This study is a Phase IV, prospective, nonrandomized, community-based study of clinical outcomes in patients with metastatic breast cancer treated with Herceptin and a taxane.

Inclusion Criteria:

• Signed informed consent
• Available tissue for central laboratory evaluation of HER2 status
• Histologically confirmed, measurable or nonmeasurable but evaluable, HER2 positive metastatic breast cancer (HER2 positive is defined as 3+ staining by IHC or gene amplification by FISH, determined by the local or central laboratory)
• Life expectancy >6 months
• Female, age >=18 years
• ECOG performance status of 0, 1, or 2
• Adequate bone marrow function as indicated by the following: *ANC >1500/uL, *Platelet count >=100,000/uL
• Adequate renal function, as indicated by creatinine <=1.5× upper limit of normal (ULN)
• Adequate liver function, as indicated by bilirubin <=1.5× ULN and AST or ALT <2× ULN unless related to primary disease
• Use of an adequate means of birth control (women of childbearing potential)

Exclusion Criteria:

• Initiation of Herceptin >=4 weeks after beginning taxane chemotherapy
• Prior chemotherapy for metastatic disease
• Prior cumulative anthracycline dose of >360 mg/m2
• History of significant cardiac disease or uncontrolled arrhythmias
• Ejection fraction of <50% or below the lower limit of normal
• Active infection
• Symptomatic or untreated brain metastases
• Pregnancy or lactation
• Concomitant malignancies or previous malignancies within the last 5 years, with the exception of adequately treated basal or squamous cell carcinoma of the skin or carcinoma in situ of the cervix
• Symptomatic intrinsic lung disease or extensive tumor involvement of the lungs, resulting in dyspnea at rest
• Hypersensitivity to study medications
• Major organ failure or systemic disease precluding the safe administration of study medications