Aspirin Prophylaxis for Venous Thromboembolism in Glioblastoma

Study Drug: Aspirin is designed to make blood less "sticky" and reduce its chances of clotting. By making blood less sticky, it may be less likely to allow a clot to form. Study Groups: If you are found to be eligible to take part in this study, you will be randomly assigned (as in the toss of a coin) to 1 of 2 study groups. If you are assigned to Group 1, you will take aspirin. If you are in Group 2, you will take a placebo. A placebo is a substance that looks like the study drug but has no active ingredients. You will have an equal chance of being placed in either group. Neither you nor your study doctor will know what group you are in. In case of an emergency, the study staff will be able to find out which group you are in. Study Drug Administration: If you are assigned to Group 1, you will take 1 aspirin tablet, once a day, by mouth. Aspirin should be taken with food and may be taken at any time during the day. If you are assigned to Group 2, you will take 1 placebo tablet once a day, by mouth. The placebo should be taken with food and may be taken at any time during the day. Study Visits: While on study you will have tests and procedures performed at the same time as each routine clinical visit and when the study doctor thinks it may be necessary. The following tests and procedures will be performed: * You will have a physical exam. * You will be checked for VTE at each visit. * Blood (2 teaspoons) will be drawn for routine tests at least once every 8 weeks. Blood samples will not be routinely collected if you are not receiving any chemotherapy. * Blood (about 1 teaspoon) will be drawn to see how well your blood clots about 4 months after you begin treatment. If you show signs of VTE, this test will be done on the first visit after the signs are shown. Length of Study: You may remain on-study for as long as you are benefiting. If the disease gets worse or intolerable side effects occur, you may be taken off of the study. End of Study Visit: Once you are off-study, you will have an end-of-study visit. At this visit, the following tests and procedures will be performed: * Your complete medical history will be recorded. * You will have a physical exam. * You will have performance status evaluation. * You will be asked about any medications you may be taking. * You will be checked for VTE. * Blood (about 1 teaspoon) will be drawn to see how well your blood clots. * If you have symptoms of VTE, you will have a Doppler ultrasound test of your legs. Follow-up: The study staff will call you or a member of your family every 3 months, after your last clinic visit, to follow your health status. This is an investigational study. Aspirin is approved by the FDA and commercially available. Its use in lowering the risk of VTE is investigational. Aspirin, and the study-related tests/procedures will be provided free of charge to you while on this study. Up to 224 patients will take part in this study. All will be enrolled at M. D. Anderson.