You will be randomly assigned (as in the toss of a coin) to one of three groups. One group will begin taking imatinib mesylate two times a day by mouth starting 7 days before surgery. The second group will start taking imatinib mesylate 5 days before surgery. Participants in the third group will begin taking imatinib mesylate 3 days before surgery. After your surgery, the removed tumor will be studied and compared to the tissue collected before surgery to see what effect (if any) imatinib mesylate had on the tumor. All patients will then continue imatinib mesylate for 2 years after surgery.