 Patients must have a histological or cytologic diagnosis of primary breast cancer with a tumour size adequate for multiple core biopsies Informed signed consent Scheduled for primary surgery Expected to be compliant for duration of study Age80 ECOG performance status 0-2 Karnofsky 60 Cardiac ejection fraction within the institutional range of normal as measured by echocardiogram or MUGA scan Eligibility of patients receiving medications known to affect, or with the potential to affect the activity or pharmacokinetics of lapatinib will be determined following review by the Trial Coordinator The effects if lapatinib on the developing fetus are unknown. For this reason, women of childbearing potential must agree to use adequate non-hormonal contraception for the duration of study participation. 