Mediastinal diffuse large cell lymphoma of B-cell type with azurophilic granules.

A case of diffuse large cell lymphoma of B-cell type with unusual azurophilic granules is reported. Lymphoma occurred primary in the upper anterior mediastinum and was suggested to be of thymic origin. Histologically, lymphoma cells showed diffuse proliferation and were large in size, frequently with multilobulated nuclei. In imprint preparations stained by May-Giemsa, most lymphoma cells had basophilic cytoplasm with azurophilic granules. Cytochemical studies showed the granules to be negative for PAS, peroxidase, acid phosphatase, and beta-glucuronidase. Electron-dense granules and electron-lucent granules were found on ultrastructural analysis. The cells were characterized as B-cell type by immunophenotypes of L26+, CD20+, CD21-, CD22+, and PCA1+, the possession of surface monotypic IgA kappa immunoglobulin, and a genotype of immunoglobulin heavy and kappa light chain gene rearrangements.