A Study of Trastuzumab-MCC-DM1 in Patients With HER2- Positive Locally Advanced or Metastatic Breast Cancer

Inclusion Criteria: * Histologically or cytologically documented breast cancer * Locally advanced or metastatic breast cancer * HER2-positive breast cancer documented as FISH-positive, IHC 3 + or CISH-positive by local laboratory assessment * Histologically or cytologically confirmed invasive breast cancer: incurable, unresectable, locally advanced breast cancer previously treated with multimodality therapy or metastatic breast cancer * Prior treatment for breast cancer in the adjuvant, unresectable, locally advanced, or metastatic setting must include both: a taxane, alone or in combination with another agent, and Trastuzumab, alone or in combination with another agent in the adjuvant, unresectable, locally advanced, or metastatic setting * Documented progression of incurable unresectable, locally advanced, or metastatic breast cancer during their most recent treatment regimen * Progression must occur during or after most recent treatment for locally advanced/metastatic breast cancer or within 6 months after completing adjuvant therapy * Adequate hematologic and end organ function * Agreement to use an effective form of birth control throughout the study * Life expectancy ≥ 90 days as assessed by the investigator Exclusion Criteria: * Less than 14 days from the first study treatment since the last anti-cancer therapy, including chemotherapy, biologic, experimental, immune, hormonal or endocrine therapy * Prior T-DM1 therapy * History of exposure to cumulative doses of select anthracyclines * History of intolerance or hypersensitivity to trastuzumab, murine proteins, or any of the excipients, that resulted in trastuzumab being permanently discontinued * Brain metastases that are untreated or progressive or currently require any type of therapy, including radiation, surgery, and/or steroids to control symptoms from brain metastases within 30 days before the first study treatment * Peripheral neuropathy of Grade ≥ 3 per National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE), version 4.0, at the time of the first study treatment * History of clinically significant cardiac dysfunction * Current known active infection with HIV, hepatitis B virus, or hepatitis C virus * Current severe, uncontrolled systemic disease * Major surgical procedure or significant traumatic injury within 28 days prior to first study treatment * Pregnancy or lactation NOTE: The site selection process has been completed. Patients can enroll at participating sites.