Patients will be randomised to a 1:1 ratio to receive either paclitaxel 80 mg/m2 IV weekly for three weeks of a four week cycle, trastuzumab 4 mg/kg loading dose and 2 mg/kg weekly IV, and oral lapatinib 1000 mg QD or paclitaxel 80 mg/m2 IV weekly for three weeks of a four week cycle, trastuzumab 4 mg/kg loading dose and 2 mg/kg weekly IV plus placebo. The primary objective of this study is to evaluate and compare time to progression (TTP). Secondary objectives will be to evaluate and compare the two treatment arms with respect to: overall response rates, clinical benefit, time to response, duration of response, progression-free survival, and overall survival. The study will first enroll an open label safety cohort of 20 patients to assess the tolerability of the triplet combination.