Search

Three cases of lympho-histiocytoid mesothelioma, a rare variant of pleural sarcomatoid malignant mesothelioma, are described. Histologically, the neoplasms were characterized by a diffuse discohesive proliferation of atypical histiocytoid cells intermixed with a marked lymphocytic and lesser plasmacytic infiltrate. One case initially was misdiagnosed as a ganglioneuroma, a second case was misinterpreted as malignant lymphoma, and a third case was sent in consultation with the differential diagnosis of inflammatory pseudotumor vs mesothelioma. Immunohistochemical studies showed strong and generalized expression of cytokeratins and vimentin by the neoplastic histiocytoid cells in all 3 cases. Two cases were positive for calretinin, one of which also was positive for HBME-1, thrombomodulin, and LeuM1. None of the cases stained with the epithelial glycoprotein markers carcinoembryonic antigen, B72.3, and Ber-EP4, or the blood group antigen, BG-8. The immunophenotype of the lymphoplasmacytic infiltrate revealed predominantly reactive, mature T cells, with fewer polytypic plasma cells, histiocytes, and B cells. In lymphohistiocytoid mesothelioma, as in the usual examples of sarcomatoid mesothelioma, the demonstration of cytokeratin expression by the neoplastic cells is the most useful diagnostic finding that allows exclusion of other neoplasms with which this entity may be confused.

We report 2 cases of follicle center non-Hodgkin lymphoma (NHL) and Warthin tumor involving the same site. Case 1 is a 68-year-old woman with Warthin tumor and grade 1 follicular NHL involving a periparotid lymph node. She had localized NHL and was treated with radiation therapy; dissemination developed 54 months later. Case 2 is a 55-year-old man with a 17-year history of a parotid mass with gradual enlargement during the last 5 years. Surgical excision revealed Warthin tumor and grade 1 follicular NHL involving the right parotid gland and surrounding lymph nodes. Immunohistochemical studies supported the diagnosis of NHL in both cases; the neoplasms were positive for CD20 and BCL-2 and negative for CD3. Polymerase chain reaction analysis done on paraffinembedded tissue of case 1 revealed monoclonal immunoglobulin heavy chain gene rearrangement and bcl-2/JH fusion DNA sequences diagnostic of the t(14;18)(q32;q21). The small size of the Warthin tumor in case 1, clearly arising in lymph node, supports the hypothesis that Warthin tumor arises from heterotopic salivary gland ducts within lymph nodes. The localized NHL in both patients suggests that the NHL initially arose in the lymph node involved by Warthin tumor, and, thus, the Warthin tumor may have provided a source of long-term antigenic stimulation from which a monoclonal B-cell population subsequently arose.

The effect of three proteases--trypsin, pepsin, and pronase--on the immunohistochemical staining of keratins with a broad-spectrum monoclonal antibody was investigated in paraffin sections of formalin and ethanol-fixed tissues by means of the peroxidase-antiperoxidase method. Both the length of exposure to the fixative and the duration of proteolysis were varied over a wide range. Ethanol-fixed tissues showed excellent preservation of the antigenicity of keratins, and no appreciable differences in immunostaining related to the length of fixation were found. The use of proteolytic enzymes did not improve these results; on the contrary, it caused rapid tissue disintegration. Formalin-fixed epithelial tissues stained weakly or failed to stain unless they were treated with a proteolytic enzyme. The optimal length of proteolysis varied with the degree of fixation; tissues that were fixed for long periods of time in formalin required longer exposure to a proteolytic enzyme and were more resistant to digestion than were tissues that were fixed briefly. No significant advantage of one protease over another was found in this study. We conclude that a proteolytic step must precede immunostaining for keratins if the tissue is fixed in formalin, but that the digestion period must be adjusted according to the length of exposure to the fixative. The superiority of alcohol over formalin fixation for the preservation of the antigenicity of keratins is confirmed by this study.

We report the identification of the human homologue of murine T200 glycoprotein. Peptide-mapping experiments suggest that the structure of the glycoprotein is highly conserved between the two species. Many of the properties of human T200 homologue are similar to those of murine T200 glycoprotein: it is broadly distributed within the hematopoietic system but is not detectable on nonhematopoietic cells; there are also structural differences between the forms of the glycoprotein found on T and B lymphoblastoid cell lines. These results suggest the homologous glycoproteins may play similar functional roles in both species.