This phase I/II trial is studying the side effects and best dose of fenretinide and to see how well it works when given together with rituximab in treating patients with B-cell non-Hodgkin lymphoma. Drugs used in chemotherapy, such as fenretinide, 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 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. Giving fenretinide together with rituximab may kill more cancer cells.