Fibril formation in the rough endoplasmic reticulum of lymphoma cells. A case report with histopathologic, immunohistochemical, electron and immunoelectron microscopic studies.

Signet ring cell lymphoma (SRCL) is a relatively new and infrequently described entity, characterized by an intracytoplasmic mass displacing the nucleus at the periphery. We present here a case of a Japanese female aged 73 with a retroperitoneal mass diagnosed as SRCL at autopsy. The neoplastic lymphoid cells showing signet ring appearance, due to the displacement of the nucleus to one side by intracytoplasmic eosinophilic inclusions, were immunoreactive for LCA, L26 and lambda light chains but PAS-negative. A small number of tumor cell nuclei demonstrated proliferating cell nuclear antigen-positive, but signet ring cells were negative. Ultrastructural study disclosed that fibrillary, lamellar or homogenous materials within rough endoplasmic reticulum of the tumor cells were selectively labeled by gold particles to anti-lambda antibody. A periodicity of 20-25 nm was observed in the fibrillary inclusions arranged haphazardly. The morphologic appearances of the case and the differential diagnosis are preceded by a review of the literature.