Transformation of nodular lymphoma to an immunoblastic IgM-producing tumor.

Two cases of nodular lymphocytic lymphoma that transformed into leukemic processes with IgM-kappa-type monoclonal proteins are reported. The transformations occurred 21 and 34 months after the diagnosis of lymphoma and were associated with rapid deterioration of the patients' conditions. The leukemic phase was characterized by plasmacytic and immunoblastic appearing lymphoid cells in the peripheral blood and marrow. Such transformation, though rare, is not unexpected in view of the currently postulated origin of nodular lymphomas in germinal center cells and of immunoglobulin-producing tumors in cells derived from germinal center cells.