Tolerability of the Combination of Lapatinib and Trastuzumab in Adults Age 60 or Older With HER2 Positive Locally Advanced or Metastatic Breast Cancer

PRIMARY OBJECTIVES: I. To estimate the safety and tolerability of the combination of trastuzumab and lapatinib (lapatinib ditosylate) in adults age 60 or older with locally advanced or metastatic breast cancer. SECONDARY OBJECTIVES: I. To describe the full toxicity profile including all grades; to estimate the rate of all grades of cardiac toxicity; to estimate the rate of all grades of diarrhea, nausea, and vomiting. II. To describe the pharmacokinetic parameters of lapatinib in older adults. III. To estimate objective response rate and clinical benefit rate as defined by modified Response Evaluation Criteria In Solid Tumors (RECIST) criteria. IV. To estimate median progression-free and overall survival. V. To explore factors other than chronological age that can affect toxicity rates as identified using a cancer-specific geriatric assessment. VI. To estimate rates of adherence to lapatinib in older adults. OUTLINE: Patients receive lapatinib ditosylate orally (PO) once daily (QD) and trastuzumab intravenously (IV) over 30-90 minutes once weekly OR once every 3 weeks. Courses repeat every 21 days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up for 30 days and then periodically thereafter.