If you are assigned to take trastuzumab and lapatinib, trastuzumab will be given by vein once every 21-day study cycle. The first infusion will be over 90 minutes. If you handle the infusion well, each additional infusion will be over 30 minutes Lapatinib will be taken by mouth every day for 21 days. You should take lapatinib on an empty stomach either 1 hour before eating or 2 hours after eating.