Comparative response assessment by total serum IgM and IgM M-component in Waldenstrom’s macroglobulinemia.

e18575 Background: Changes in total IgM and the electrophoretically determined IgM M-component are used as surrogate serum response markers in Waldenstrom’s Macroglobulinemia (WM). Their ability to reflect underlying disease burden changes have not been compared. Methods: 73 rituximab-naive patients were studied who underwent rituximab-based therapy on a study, and for whom serial total serum IgM levels, IgM M-component, and bone marrow (BM) assessments were available. Baseline: Median age 61 years; serum IgM 3,960 mg/dL; IgM M-component 2.55 g/dL; BM disease by core biopsy 60%. 5 patients had serum IgM levels 5,000 mg/dL. 39 patients had adenopathy and/or splenomegaly by baseline CT scans. Post-therapy, serum IgM declined from 3,960 to 1,800 mg/dL (p<0.0001); IgM M-component from 2.55 to 1.28 g/dL (p<0.0001); and BM involvement from 60% to 10% (p<0.0001). Among 39 patients with extramedullary disease, post-therapy CT scans were improved for 18, unchanged for 14, and worse for 7. Re...