Waldenstrom Macroglobulinemia (lymphoplasmacytic lymphoma, WM) is a low-grade lymphoplasmacytic lymphoma characterized by the involvement of the bone marrow with lymphoplasmacytic cells and the production of immunoglobulin M monoclonal protein in the circulation . Waldenstrom Macroglobulinemia is characterized by anemia and cytopenias due in part to the clonal expansion in the bone marrow. In addition, infiltration of the liver, spleen, and lymph nodes may occur in 15-20% of the patients leading to enlargement of these organs. Finally, complications related to elevated serum monoclonal protein such as hyperviscosity may also occur. Waldenstrom macroglobulinemia is an incurable disease with an overall median survival of 5-6 years from the development of symptoms . The median age at diagnosis is 63 years Options of therapy in patients with relapsed/refractory Waldenstrom Macroglobulinemia include rituximab, alkylating agents, nucleoside analogues. Although novel agents, such as bortezomib and thalidomide, are still matter of debate, several phase II studies have demonstrated that novel agents, especially Bortezomib, are active agent in relapsed and refractory Waldenstrom Macroglobulinemia .The overall response rate in single agents bortezomib studies reach 80%, with major responses observed in 30-40% of patients. Therefore, there is a need to identify new therapeutic agents for Waldenstrom Macroglobulinemia patients.

In view of their success in the treatment of patients with Multiple Myeloma, immunomodulatory drugs (IMiDS) were tested in patients with Waldenstrom Macroglobulinemia, although their experience is limited. Thalidomide is nonmyelosuppressive, immunomodulatory, and antiangiogenic and may be a reasonable choice for patients for whom first-line therapies have failed, those who have had disease relapse and are not candidates for alkylating or nucleoside analogue therapy, or patients with pancytopenia . Twenty three Waldenstrom Macroglobulinemia patients were evaluable in a phase II study of thalidomide in combination with rituximab. Although the overall and major response rates were of 78% and 70%, respectively; tolerance was a concern, and dose reduction of thalidomide occurred in all patients and led to discontinuation in 11 patients.

Lenalidomide has been studied in Multiple Myeloma and myelodysplastic syndrome and found to be more potent and also to lack the neurotoxic and prothrombotic adverse effects of thalidomide . Based on the potent activity of lenalidomide in Multiple Myeloma and the lack of neuropathy with this agent, and based on the interesting results reported with thalidomide-rituximab phase II tril in relapse/refractory Waldenstrom Macroglobulinemia, a phase II study of lenalidomide 25mg daily in combination with rituximab was perform in patients with relapsed/refractory Waldenstrom Macroglobulinemia. Lenalidomide was administered for 3 weeks, followed by a one week pause for an intended duration of 48 weeks. Patients received one week of therapy with lenalidomide, after which rituximab (375mg/m2) was administered weekly on weeks 2-5, then 13-16 . Twelve patients were evaluable for an overall and a major response rate of 67% and 33%, and a median time to progression of 15.6 months. Acute decreases in hematocrit were observed during first 2 weeks of lenalidomide therapy in 13/16 (81%) patients with a median hematocrit decrease of 4.4% (1.7-7.2%). Despite reduction of initiation doses to 5mg daily, anemia continued to be problematic without evidence of hemolysis or more general myelosuppression. Therefore, the mechanism for pronounced anemia in Waldenstrom Macroglobulinemia patients receiving lenalidomide remains to be determined and the use of this agent among Waldenstrom Macroglobulinemia patients remains investigational.