Purpose

RATIONALE: Drugs used in chemotherapy such as cyclophosphamide, prednisone, and methylprednisolone use different ways to stop cancer cells from dividing so they stop growing or die. Monoclonal antibodies such as rituximab can locate cancer cells and either kill them or deliver cancer-killing substances to them without harming normal cells. Combining cyclophosphamide and either prednisone or methylprednisolone with rituximab may be effective in treating lymphoproliferative disease following organ transplantation. PURPOSE: Phase II trial to study the effectiveness of combining cyclophosphamide and either prednisone or methylprednisolone with rituximab in treating patients who have Epstein-Barr virus-positive lymphoproliferative disease following organ transplantation.