The FB-10 study is designed as an open label, single arm, Phase Ib/II study with a dose-escalation phase and an expanded cohort (phase II) to evaluate the combination of trastuzumab emtansine (T-DM1) with neratinib in women with metastatic, HER2-positive breast cancer. The primary aim of the phase Ib portion of this study is to determine the safety and tolerability of the two-drug combination. The primary aim of the phase II portion is to demonstrate efficacy.