Short-term Presurgical Study to Assess Molecular Predictors of Lapatinib's Effects in Primary Breast Cancer

Inclusion Criteria:

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 Age\<80 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.

Able to swallow and retain oral medication.

Exclusion Criteria:

Patients with prior diagnosis of malignancy except in situ disease or basal cell carcinoma of the skin.

Patients may be receiving any other investigational agents or receiving concurrent anticancer therapy. In addition, all herbal (alternative) medicines are excluded.

Evidence of metastatic disease. Use of hormonal therapy such as oral contraceptives or hormonal replacement therapy within 4 weeks of study entry.

Regular use of steroid hormones or other agents that could influence study endpoints History of allergic reactions attributed to compounds of similar chemical or biologic composition to GW572016.

Uncontrolled inter-current illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/ social situations that would limit compliance with study requirements.