4-1BB Agonist Monoclonal Antibody PF-05082566 With Trastuzumab Emtansine or Trastuzumab in Treating Patients With Advanced HER2-Positive Breast Cancer

PRIMARY OBJECTIVE: Estimate the maximum tolerated dose (MTD) and determine the recommended dose (RP2D) of utomilumab in combination with ado-rastuzumab emtansine (T-DM1) or trastuzumab in subjects with HER2-positive advanced breast cancer. SECONDARY OBJECTIVES: * Determine the objective tumor response (ORR) * Determine the time to tumor response (TTR) * Determine the duration of response (DR) * Determine progression free survival (PFS) * Assess the safety and tolerability of utomilumab in combination with ado-trastuzumab emtansine or trastuzumab OUTLINE: Patients are randomized to 1 of 2 cohorts. COHORT 1: Dose 1: Utomilumab 20 mg IV + ado-trastuzumab emtansine (T-DM1) 3.6 mg/kg IV every 3 weeks. Dose 2: Dose Level 2 - Utomilumab 100 mg IV + ado-trastuzumab emtansine 3.6 mg/kg IV every 3 weeks COHORT 2: Dose 1: Utomilumab 20 mg IV + trastuzumab 6 mg/kg IV every 3 weeks. Dose Level 2 - Utomilumab 100 mg IV + trastuzumab 6 mg/kg IV every 3 weeks.