 RATIONALE: Drugs used in chemotherapy, such as bendamustine, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. 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. Giving bendamustine together with rituximab may kill more cancer cells. 