Assessment of bone marrow response in Waldenström's macroglobulinemia.

In this study we used bone marrow flow cytometry and immunohistochemistry to evaluate response to fludarabine therapy in patients with Waldenström's macroglobulinemia (WM)/lymphoplasmacytic lymphoma. Responses in serum M protein were typically delayed with a median time to maximum response of 6 months following the completion of therapy (range, 0-18 months). In contrast, bone marrow responses occurred promptly in responding patients such that there were no detectable clonal B cells at the end of therapy in 55% of patients assessed. Persistent monoclonal plasma cells were, however, readily identified by CD138 immunohistochemistry, explaining the persistence of serum M protein in these patients. This simple observation has significant implications for the assessment of responses in WM as well as the design of future therapeutic strategies.