Lapatinib is an anti-cancer drug that is approved by the Food and Drug Administration (FDA) for the treatment of metastatic HER2-positive breast cancer. HER2 is a protein involved in the growth of some cancer cells. In lab tests and small clinical studies, lapatinib is also found to kill other types of cancer that have another related protein called epidermal growth factor receptor (EGFR). For participants who have other cancers, the use of lapatinib in this study is investigational. This means the drug is not FDA approved for this use.