RATIONALE: Drugs used in chemotherapy, such as methotrexate and leucovorin, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Glucarpidase may help return the level of methotrexate in the blood to a safe range. Giving high-dose methotrexate together with glucarpidase and leucovorin may kill more cancer cells.