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A peripheral T-cell lymphoma with a high content of epithelioid cells-an entity that reveals morphologic and clinical characteristics resembling those seen in angioimmunoblastic lymphadenopathy (AILD)-was separated from lymphoepithelioid cell lymphoma (Lennert's lymphoma, or LeL); it was considered a variant of the AILD type of peripheral T-cell lymphoma (AILD-PTCLep). A histologic evaluation of 135 lymph node biopsies from 98 patients with AILD-PTCLep showed that AILD-PTCLep and LeL share certain features, but there are also differences between the two. A finding common to both lymphomas was the mixture of neoplastic T-lymphocytes and a large number of epithelioid cells, which accumulated mostly in small, poorly defined clusters. Additionally, typical Sternberg-Reed and Hodgkin cells as well as giant cells resembling them were observed only rarely in either of these lymphomas. In contrast to LeL, AILD-PTCLep showed a great increase in follicular dendritic cells, which were sometimes identifiable in routine slides as so-called burned-out germinal centers. In AILD-PTCLep, the number of small vessels (predominantly epithelioid venules) and fibers is also usually greatly increased, whereas in LeL this is not the case, or the increase is only slight. Hypocellular and lymphocyte-depleted areas and PAS-positive intercellular material were seen in AILD-PTCLep (18% and 34%, respectively), but not in LeL. Large numbers of eosinophils, plasma cells and plasma cell precursors, and diffuse neoplastic infiltration of the capsule and extranodal tissue were observed much more commonly in AILD-PTCLep. Corresponding to these differences in the histologic pictures are differences in the clinical pictures. Hyperimmune phenomena (pruritus, skin rash, hemolytic anemia, allergy to antibiotics) and hypergammaglobulinemia were much more common in AILD-PTCLep than in LeL. Allergy to chemotherapeutic agents was observed only in AILD-PTCLep patients. Carcinomas were observed as a second neoplasm in 11% of the patients with AILD-PTCLep, but not at all in LeL. The similarities between the two lymphomas include the age and sex distribution (peak in the seventh decade and slight predominance of the male sex) and a similar median survival time. Another similarity is the possibility that the disease will develop into a large-cell malignant lymphoma. This was observed in 13% of the cases of AILD-PTCLep and 8% of the cases of LeL.