RATIONALE: Monoclonal antibodies, such as rituximab, can block cancer cell growth in different ways. Some block the ability of cancer cells to grow and spread. Others find cancer cells and help kill them or carry cell-killing substances to them. Drugs used in chemotherapy, such as bendamustine hydrochloride, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Lenalidomide may stop the growth of cancer by blocking blood flow to the tumor. Giving rituximab together with bendamustine hydrochloride and lenalidomide may kill more cancer cells.