Purpose

RATIONALE: Monoclonal antibodies, such as rituximab, can block cancer growth in different ways. Some find cancer cells and kill them or carry cancer-killing substances to them. Others interfere with the ability of cancer cells to grow and spread. Drugs used in chemotherapy, such as methotrexate, leucovorin, vincristine, procarbazine, dexamethasone, and cytarabine, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Giving rituximab together with combination chemotherapy may kill more cancer cells. PURPOSE: This phase II trial is studying how well giving rituximab together with combination chemotherapy works in treating patients with primary central nervous system (CNS) lymphoma.