Participants in this study will take Imatinib Mesylate by mouth in a single dose on a daily basis. Participants will be treated for 6 weeks, which is one cycle of therapy. After 6 weeks, participants will be evaluated for side effects and tumor response. The dose may be decreased for the next cycle if participants side effects. Participants will be removed from the study if the tumor gets worse. Participants may remain on the study as long as the tumor has not gotten worse and there are no intolerable side effects.