RATIONALE: Drugs used in chemotherapy, such as melphalan and dexamethasone, work in different ways to stop the growth of abnormal plasma cells, either by killing the cells or by stopping them from dividing. Biological therapies, such as lenalidomide, may stimulate the immune system in different ways and stop the abnormal plasma cells from growing. Giving melphalan together with lenalidomide and dexamethasone may be an effective treatment for primary systemic amyloidosis.