RATIONALE: Drugs used in chemotherapy, such as prednisolone and dexamethasone, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Giving more than one drug (combination chemotherapy) may kill more cancer cells. It is not yet known whether prednisolone is more effective than dexamethasone when given together with combination chemotherapy in treating lymphoblastic lymphoma.