This randomized phase II trial studies how well rituximab and combination chemotherapy with or without lenalidomide works in treating patients with newly diagnosed stage II-IV diffuse large B cell lymphoma. 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. Drugs used in chemotherapy, such as cyclophosphamide, doxorubicin hydrochloride, vincristine sulfate, and prednisone, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Lenalidomide may stimulate the immune system in different ways and stop cancer cells from growing. It is not yet known whether rituximab and combination chemotherapy are more effective when given with or without lenalidomide in treating patients with diffuse large B cell lymphoma.