RATIONALE: Lenalidomide may stop the growth of cancer by blocking blood flow to the tumor. Monoclonal antibodies, such as rituximab, can block cancer 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 cancer-killing substances to them. Giving lenalidomide together with rituximab may be an effective treatment for B-cell non-Hodgkin lymphoma.