Emergence of immunoblastic sarcoma in Waldenstrom's macroglobulinemia.

A case involving a 65-year-old man with Waldenstrom's macroglobulinemia (WMG) which transformed into immunoblastic sarcoma is presented. Surface IgM (kappa) was demonstrated on the plasmacytoid lymphocytes of the bone marrow at presentation as well as on the less differentiated cells of the immunoblastic sarcoma. Serum IgM levels fell at the time that immunoblastic transformation occurred. This case illustrates the fact that a fall in serum paraprotein may herald a malignant transformation of WMG.