This study will examine the inhibition of ErbB1 and ErbB2 phosphorylation and downstream mediators of tumor cell growth and survival tumor tissue in treatment-naive breast cancer patients for three dosing schedules of lapatinib.

Inclusion criteria:

• Clinical labs are within acceptable ranges.
• A histologically confirmed, treatment-naive, breast tumor measuring 1 cm or greater that can be readily biopsied.
• At least 18 years of age.
• Females must meet certain criteria specified in protocol.
• Ability to swallow and retain oral medication.
• Ability to follow and understand directions.

Exclusion criteria:

• Female who is pregnant or lactating.
• Medically unfit by the doctor as a result of the medical interview or physicals.
• Received treatment of an investigational drug within 4 weeks of study start.
• Currently receiving treatment with prohibited meds listed in protocol.
• Had major surgery in previous 2 weeks.
• Had prior radiation therapy to the chest to treat this incidence of breast cancer.
• Hypersensitivity reaction or idiosyncrasy to drugs chemically related to the study med.
• Has a malabsorption syndrome.