Eribulin With Trastuzumab as First-line Therapy for Locally Recurrent or Metastatic HER2 Positive Breast Cancer

Key Inclusion criteria: * Age 18 years or older * Histologically or cytologically proven adenocarcinoma of the breast * Subjects who have locally recurrent or metastatic disease with at least one measurable lesion * HER2 positive as determined by score of 3 on immunohistochemistry (IHC) staining or gene amplification by fluorescence in situ hybridization (FISH). * Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0, 1 or 2 * At least 12 months since prior neoadjuvant or adjuvant chemotherapy * At least 2 weeks since prior radiotherapy, endocrine therapy, trastuzumab, or lapatinib, with complete recovery from the effects of these interventions * Adequate renal function * Adequate bone marrow function * Adequate liver function * Adequate cardiac function Key Exclusion criteria: * Prior chemotherapy, biologic therapy, or investigational therapy for locally recurrent or metastatic HER2 breast cancer. * Subjects who have had a prior malignancy other than carcinoma in situ of the cervix, or nonmelanoma skin cancer * Prior exposure to greater than 360 mg/m2 doxorubicin or liposomal doxorubicin, greater than 120 mg/m2 mitoxantrone, greater than 90 mg/m2 idarubicin, or greater than 720 mg/m2 epirubicin * Inflammatory breast cancer * Prior history of hypertensive crisis or hypertensive encephalopathy * Clinically significant cardiovascular impairment * Subjects with known central nervous system (CNS) disease are not eligible, except for those subjects with t…