You will also receive small doses of methotrexate and Ara-C by a spinal tap to help prevent relapse of the disease in the fluid surrounding your brain. A spinal tap requires the insertion of a needle through the skin and the soft tissues of the lower back to reach a pocket of fluid that is a part of the fluid space that surrounds the brain and the spinal cord. Once the fluid space is reached, a sample of the fluid will be collected. The procedure is done under local anesthesia. It can also be used to give chemotherapy. You may be given treatment with methotrexate and Ara-C, alternately, to the brain by spinal tap during each cycle for a total 6-8 doses. The number of doses you receive will depend on how many doses the study doctor thinks is necessary. If you start with leukemia in the brain, it will be given 2 times a week until there is no leukemia present and then 1 time a week for 4 weeks. Occasionally, a sample of the fluid obtained from the spinal taps may be examined by sensitive tests for presence of leukemia. A sample will also be sent to determine the amount of dasatinib to see if it reaches the fluid around the brain.