Typical Waldenstrom macroglobulinemia is derived from a B-cell arrested after cessation of somatic mutation but prior to isotype switch events

There exists a wide spectrum of IgM-secreting B-cell tumors with different clinical behavior. Knowledge of the V(H) gene status can reveal their origin and clonal history. For Waldenstrom macroglobulinemia (WM), a distinct subtype of lymphoplasmacytic lymphoma, early data on limited sequences showed evidence for somatic mutation. A recent report of one case demonstrated intraclonal mutational activity occurring after transformation, a characteristic of germinal center lymphomas. To extend the investigation, we have analyzed 7 cases of WM. V(H) genes were somatically mutated with no evidence of intraclonal variation in all cases. In contrast to IgM-secreting multiple myeloma, there was no evidence for isotype switch transcripts in any of the cases. These data support the concept that typical WM is derived from a B cell that has undergone somatic mutation prior to transformation, at a point where isotype switch events have not been initiated. (Blood. 2002;100:1505-1507)