Rituximab Plus Cyclophosphamide in Treating Patients With Indolent Stage III or Stage IV Non-Hodgkin's Lymphoma

RATIONALE: Monoclonal antibodies can locate cancer cells and either kill them or deliver cancer-killing substances to them without harming normal cells. Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die. Combining chemotherapy and monoclonal antibody therapy may kill more cancer cells. PURPOSE: Phase II trial to study the effectiveness of rituximab plus cyclophosphamide in treating patients who have indolent stage III or stage IV non-Hodgkin's lymphoma.