Purpose: Follicular lymphoma (FL) is the most common subtype of indolent lymphomas. Rituximab is widely used alone or in combination therapy for the treatment of FL. Despite its wellestablished clinical efficacy, a subpopulation of patients does not respond to rituximab and most patients will relapse after therapy. The mechanisms of action and resistance to rituximab are not fully understood. Experimental Design: To study these mechanisms we developed an in vivo model of FL resistant to rituximab.This model was developed using the human RL line, isolated from a patient with FL, grown as xenotransplants in severe combined immunodeficient mice, exposed weekly to rituximab in vivo, followed by serial reimplantation and reexposure to rituximab, until a resistant phenotype was obtained. Results: RL-derived tumors unexposed to rituximab were grown as controls and compared with the resistant tumors. Although the expression of CD46 and CD55 antigens were not differently expressed in the resistant cells, the complement inhibitor CD59 was overexpressed in a subpopulation and CD20 was found to be expressed at a lower level in a minority of cells. Bcl-X L andYY1 were also found more highly expressed in rituximab-resistant cells. Conclusion:This model provides insight on potential in vivo resistance mechanisms to rituximab and could help contribute to the development of novel therapies in rituximab-refractory diseases.

The serum IgM level has been utilised as a marker of tumor progression and to assess response to therapy in patients with Waldenstrom macroglobulinemia (WM). However, there are many limitations to the IgM protein level. The objective of this study was to evaluate the association of known tumor burden markers and prognostic factors with serum free light chain (sFLC) in 98 patients with WM. We demonstrated that sFLC measurement accurately differentiated IgM-MGUS compared with WM reflecting a measurement of tumor burden. In univariate and multivariate analysis, median sFLC at the cut-off at 60 mg/L was higher for WM patients with low hemoglobin and high b2M, when we applied the WM-IPSS cut-offs, but showed no association with IgM level. This study demonstrates that sFLC is a new marker in WM disease. Further analysis is required to prospectively study the role of sFLC in monitoring response to therapy and as a prognostic marker in WM patients.

In the past years, new developments have occurred both in the understanding of the biology of Waldenstrom Macroglobulinemia (WM) and in therapeutic options for WM. WM is a B-cell disorder characterized primarily by bone marrow infiltration with lymphoplasmacytic cells, along with demonstration of an IgM monoclonal gammopathy. Despite advances in therapy, WM remains incurable, with 5-6 years median overall survival of patients in symptomatic WM. Therapy is postponed for asymptomatic patients, and progressive anemia is the most common indication for initiation of treatment. The main therapeutic options include alkylating agents, nucleoside analogues, and rituximab. Studies involving combination chemotherapy are ongoing, and preliminary results are encouraging. No specific agent or regimen has been shown to be superior to another for treatment of WM. As such, novel therapeutic agents are needed for the treatment of WM. In ongoing efforts, we and others have sought to exploit advances made in the understanding of the biology of WM so as to better target therapeutics for this malignancy. These efforts have led to the development of several novel agents including the proteasome inhibitor bortezomib, and several Akt/mTor inhibitors, perifosine and Rad001, and immunomodulatory agents such as thalidomide and lenalidomide. Studies with monoclonal antibodies are ongoing and promising including the use of alemtuzumab, SGN-70, and the APRIL/BLYS blocking protein TACI-Ig atacicept. Other agents currently being tested in clinical trials include the PKC inhibitor enzastaurin, the natural product resveratrol, as well as the statin simvastatin. This report provides an update of the current preclinical studies and clinical efforts for the development of novel agents in the treatment of WM.

PINI index appears to be a useful and easy-to-perform marker in routine to determine the prognosis of patients with MM, especially in the elderly population. PINI might represent an alternative to ISS score, especially in elderly patients, in the future.