A Study of Trastuzumab-MCC-DM1 Administered Intravenously to Patients With HER2-Positive Metastatic Breast Cancer Who Have Previously Received a Trastuzumab-Containing Regimen

Inclusion Criteria:

* Histologically documented, incurable, locally advanced or metastatic breast cancer
* Evaluable or measurable HER2-positive disease
* History of progression during or within 60 days after treatment with any prior trastuzumab-containing chemotherapy regimen for HER2-positive breast cancer
* Previous treatment with chemotherapy for MBC
* Granulocyte count ≥ 1,500/μL, platelet count ≥ 100,000/μL, and hemoglobin ≥ 9 g/dL
* Serum bilirubin ≤ 1.5 mg/dL; AST, ALT, and alkaline phosphatase ≤ 2.5 × upper limit of normal (ULN) except for: Patients with hepatic metastases: ALT and AST ≤ 5 × ULN Patients with hepatic and/or bone metastases: alkaline phosphatase ≤ 5 × ULN
* Serum creatinine ≤ 1.5 mg/dL or creatinine clearance of ≥ 60 mL/min based on a 24-hour urine collection
* Eastern Cooperative Oncology Group (ECOG) Performance Status of 0, 1, or 2
* Women of childbearing potential and men must agree to use an effective method of birth control (e.g., hormonal, barrier) while receiving study treatment

Exclusion Criteria:

* History of significant cardiac disease, unstable angina, CHF, myocardial infarction, or ventricular arrhythmia requiring medication
* History of Grade ≥ 3 hypersensitivity reaction to trastuzumab
* History of any toxicity to trastuzumab that resulted in trastuzumab being permanently discontinued
* Symptomatic brain metastases or any radiation or surgery for brain metastases within 3 months of first study treatment
* Require supplemental oxygen for daily activities
* Grade ≥ 2 peripheral neuropathy
* Bisphosphonate therapy for symptomatic hypercalcemia
* Any chemotherapy, hormonal therapy, radiotherapy, immunotherapy, or biologic therapy for the treatment of breast cancer within 4 weeks of first study treatment
* Any experimental therapy within 4 weeks of first study treatment
* Any major surgical procedure within 4 weeks of first study treatment
* History of clinically symptomatic liver disease, including viral or other hepatitis, current or history of alcoholism, or cirrhosis
* Pregnancy or lactation
* Cardiac troponin I ≥ 0.2 ng/mL
* Ejection fraction \< 50% or below the lower limit of normal determined by echocardiogram or MUGA scan
* Prior cumulative doxorubicin dose of \> 360 mg/m2 or equivalent