Histiocytic lymphoma in a patient with Lennert's lymphoma. Report of a case with unusual cytoplasmic inclusions.

The transformation of Lennert's lymphoma into histiocytic lymphoma appears to be part of the natural history of the disorder rather than therapeutically induced. Unusual paranuclear nonmembrane-bound filamentous inclusions were found in many of the neoplastic cells in the histiocytic lymphoma. We report evidence for the immunoglobulin nature of this material, indicating a B cell origin of the neoplasm.